Provides information about how to manage storage devices on a SUSE Linux Enterprise Server.
- About This Guide
- I File Systems and Mounting
- 1 Overview of File Systems in Linux
- 1.1 Terminology
- 1.2 Btrfs
- 1.3 XFS
- 1.4 Ext2
- 1.5 Ext3
- 1.6 Ext4
- 1.7 ReiserFS
- 1.8 tmpfs
- 1.9 Other Supported File Systems
- 1.10 Blacklisted file systems
- 1.11 Large File Support in Linux
- 1.12 Linux Kernel Storage Limitations
- 1.13 Freeing unused file system blocks
- 1.14 Troubleshooting File Systems
- 1.15 Additional Information
- 2 Resizing File Systems
- 3 Mounting storage devices
- 4 Multi-tier Caching for Block Device Operations
- 1 Overview of File Systems in Linux
- II Logical Volumes (LVM)
- 5 LVM Configuration
- 5.1 Understanding the Logical Volume Manager
- 5.2 Creating Volume Groups
- 5.3 Creating Logical Volumes
- 5.4 Automatically Activating Non-Root LVM Volume Groups
- 5.5 Resizing an Existing Volume Group
- 5.6 Resizing a Logical Volume
- 5.7 Deleting a Volume Group or a Logical Volume
- 5.8 Disabling LVM on boot
- 5.9 Using LVM Commands
- 5.10 Tagging LVM2 Storage Objects
- 6 LVM Volume Snapshots
- 5 LVM Configuration
- III Software RAID
- IV Network Storage
- 14 iSNS for Linux
- 15 Mass Storage over IP Networks: iSCSI
- 15.1 Installing the iSCSI LIO Target Server and iSCSI Initiator
- 15.2 Setting Up an iSCSI LIO Target Server
- 15.3 Configuring iSCSI Initiator
- 15.4 Setting Up Software Targets Using targetcli-fb
- 15.5 Using iSCSI Disks when Installing
- 15.6 Troubleshooting iSCSI
- 15.7 iSCSI LIO Target Terminology
- 15.8 Additional Information
- 16 Fibre Channel Storage over Ethernet Networks: FCoE
- 17 NVMe-oF
- 18 Managing Multipath I/O for Devices
- 18.1 Understanding Multipath I/O
- 18.2 Hardware Support
- 18.3 Planning for Multipathing
- 18.4 Installing SUSE Linux Enterprise Server on multipath systems
- 18.5 Updating SLE on multipath systems
- 18.6 Multipath management tools
- 18.7 Configuring the System for Multipathing
- 18.8 Multipath configuration
- 18.9 Configuring policies for failover, queuing, and failback
- 18.10 Configuring path grouping and priorities
- 18.11 Selecting devices for multipathing
- 18.12 Multipath device names and WWIDs
- 18.13 Miscellaneous options
- 18.14 Best Practice
- 18.15 Troubleshooting MPIO
- 19 Managing Access Control Lists over NFSv4
- A GNU licenses
- 1.1 File System Types in Linux
- 1.2 Maximum Sizes of Files and File Systems (On-Disk Format, 4 KiB Block Size)
- 1.3 Storage Limitations
- 2.1 File System Support for Resizing
- 7.1 Comparison of RAID 5 and RAID 6
- 9.1 Nested RAID Levels
- 9.2 Scenario for Creating a RAID 10 (1+0) by Nesting
- 9.3 Scenario for Creating a RAID 10 (0+1) by Nesting
- 9.4 Complex RAID 10 compared to Nested RAID 10
- 9.5 Scenario for Creating a RAID 10 Using mdadm
- 11.1 Tasks Involved in Resizing a RAID
- 11.2 Scenario for Increasing the Size of Component Partitions
- 12.1 Translation between Non-SES-2 Patterns and SES-2 Patterns
Copyright © 2006–2024 SUSE LLC and contributors. All rights reserved.
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or (at your option) version 1.3; with the Invariant Section being this copyright notice and license. A copy of the license version 1.2 is included in the section entitled “GNU Free Documentation License”.
For SUSE trademarks, see https://www.suse.com/company/legal/. All third-party trademarks are the property of their respective owners. Trademark symbols (®, ™ etc.) denote trademarks of SUSE and its affiliates. Asterisks (*) denote third-party trademarks.
All information found in this book has been compiled with utmost attention to detail. However, this does not guarantee complete accuracy. Neither SUSE LLC, its affiliates, the authors nor the translators shall be held liable for possible errors or the consequences thereof.
About This Guide #
This guide provides information about how to manage storage devices on SUSE Linux Enterprise Server 15 SP2. For information about partitioning and managing devices, see Book “Deployment Guide”, Chapter 10 “Expert Partitioner”. This guide is intended for system administrators.
1 Available documentation #
- Online documentation
Our documentation is available online at https://documentation.suse.com. Browse or download the documentation in various formats.
Note: Latest updatesThe latest updates are usually available in the English-language version of this documentation.
- SUSE Knowledgebase
If you have run into an issue, also check out the Technical Information Documents (TIDs) that are available online at https://www.suse.com/support/kb/. Search the SUSE Knowledgebase for known solutions driven by customer need.
- Release notes
For release notes, see https://www.suse.com/releasenotes/.
- In your system
For offline use, the release notes are also available under
/usr/share/doc/release-notes
on your system. The documentation for individual packages is available at/usr/share/doc/packages
.Many commands are also described in their manual pages. To view them, run
man
, followed by a specific command name. If theman
command is not installed on your system, install it withsudo zypper install man
.
2 Improving the documentation #
Your feedback and contributions to this documentation are welcome. The following channels for giving feedback are available:
- Service requests and support
For services and support options available for your product, see https://www.suse.com/support/.
To open a service request, you need a SUSE subscription registered at SUSE Customer Center. Go to https://scc.suse.com/support/requests, log in, and click .
- Bug reports
Report issues with the documentation at https://bugzilla.suse.com/.
To simplify this process, click the
icon next to a headline in the HTML version of this document. This preselects the right product and category in Bugzilla and adds a link to the current section. You can start typing your bug report right away.A Bugzilla account is required.
- Contributions
To contribute to this documentation, click the
icon next to a headline in the HTML version of this document. This will take you to the source code on GitHub, where you can open a pull request.A GitHub account is required.
Note:only available for EnglishThe
icons are only available for the English version of each document. For all other languages, use the icons instead.For more information about the documentation environment used for this documentation, see the repository's README.
You can also report errors and send feedback concerning the documentation to <doc-team@suse.com>. Include the document title, the product version, and the publication date of the document. Additionally, include the relevant section number and title (or provide the URL) and provide a concise description of the problem.
3 Documentation conventions #
The following notices and typographic conventions are used in this document:
/etc/passwd
: Directory names and file namesPLACEHOLDER: Replace PLACEHOLDER with the actual value
PATH
: An environment variablels
,--help
: Commands, options, and parametersuser
: The name of a user or grouppackage_name: The name of a software package
Alt, Alt–F1: A key to press or a key combination. Keys are shown in uppercase as on a keyboard.
AMD/Intel This paragraph is only relevant for the AMD64/Intel 64 architectures. The arrows mark the beginning and the end of the text block.
IBM Z, POWER This paragraph is only relevant for the architectures
IBM Z
andPOWER
. The arrows mark the beginning and the end of the text block.Chapter 1, “Example chapter”: A cross-reference to another chapter in this guide.
Commands that must be run with
root
privileges. You can also prefix these commands with thesudo
command to run them as a non-privileged user:#
command
>
sudo
command
Commands that can be run by non-privileged users:
>
command
Commands can be split into two or multiple lines by a backslash character (
\
) at the end of a line. The backslash informs the shell that the command invocation will continue after the line's end:>
echo
a b \ c dA code block that shows both the command (preceded by a prompt) and the respective output returned by the shell:
>
command
outputNotices
Warning: Warning noticeVital information you must be aware of before proceeding. Warns you about security issues, potential loss of data, damage to hardware, or physical hazards.
Important: Important noticeImportant information you should be aware of before proceeding.
Note: Note noticeAdditional information, for example about differences in software versions.
Tip: Tip noticeHelpful information, like a guideline or a piece of practical advice.
Compact Notices
Additional information, for example about differences in software versions.
Helpful information, like a guideline or a piece of practical advice.
4 Support #
Find the support statement for SUSE Linux Enterprise Server and general information about technology previews below. For details about the product lifecycle, see https://www.suse.com/lifecycle.
If you are entitled to support, find details on how to collect information for a support ticket at https://documentation.suse.com/sles-15/html/SLES-all/cha-adm-support.html.
4.1 Support statement for SUSE Linux Enterprise Server #
To receive support, you need an appropriate subscription with SUSE. To view the specific support offers available to you, go to https://www.suse.com/support/ and select your product.
The support levels are defined as follows:
- L1
Problem determination, which means technical support designed to provide compatibility information, usage support, ongoing maintenance, information gathering and basic troubleshooting using available documentation.
- L2
Problem isolation, which means technical support designed to analyze data, reproduce customer problems, isolate a problem area and provide a resolution for problems not resolved by Level 1 or prepare for Level 3.
- L3
Problem resolution, which means technical support designed to resolve problems by engaging engineering to resolve product defects which have been identified by Level 2 Support.
For contracted customers and partners, SUSE Linux Enterprise Server is delivered with L3 support for all packages, except for the following:
Technology previews.
Sound, graphics, fonts, and artwork.
Packages that require an additional customer contract.
Some packages shipped as part of the module Workstation Extension are L2-supported only.
Packages with names ending in -devel (containing header files and similar developer resources) will only be supported together with their main packages.
SUSE will only support the usage of original packages. That is, packages that are unchanged and not recompiled.
4.2 Technology previews #
Technology previews are packages, stacks, or features delivered by SUSE to provide glimpses into upcoming innovations. Technology previews are included for your convenience to give you a chance to test new technologies within your environment. We would appreciate your feedback. If you test a technology preview, please contact your SUSE representative and let them know about your experience and use cases. Your input is helpful for future development.
Technology previews have the following limitations:
Technology previews are still in development. Therefore, they may be functionally incomplete, unstable, or otherwise not suitable for production use.
Technology previews are not supported.
Technology previews may only be available for specific hardware architectures.
Details and functionality of technology previews are subject to change. As a result, upgrading to subsequent releases of a technology preview may be impossible and require a fresh installation.
SUSE may discover that a preview does not meet customer or market needs, or does not comply with enterprise standards. Technology previews can be removed from a product at any time. SUSE does not commit to providing a supported version of such technologies in the future.
For an overview of technology previews shipped with your product, see the release notes at https://www.suse.com/releasenotes.
Part I File Systems and Mounting #
- 1 Overview of File Systems in Linux
SUSE Linux Enterprise Server ships with different file systems from which to choose, including Btrfs, Ext4, Ext3, Ext2 and XFS. Each file system has its own advantages and disadvantages. For a side-by-side feature comparison of the major file systems in SUSE Linux Enterprise Server, see https://www.suse.com/releasenotes/x86_64/SUSE-SLES/15-SP2/#allArch-filesystems (File System Support and Sizes). This chapter contains an overview of how these file systems work and what advantages they offer.
- 2 Resizing File Systems
Resizing file systems—not to be confused with resizing partitions or volumes—can be used to make space available on physical volumes or to use additional space available on a physical volume.
- 3 Mounting storage devices
This section gives an overview which device identificators are used during mounting of devices, and provides details about mounting network storages.
- 4 Multi-tier Caching for Block Device Operations
A multi-tier cache is a replicated/distributed cache that consists of at least two tiers: one is represented by slower but cheaper rotational block devices (hard disks), while the other is more expensive but performs faster data operations (for example SSD flash disks).
1 Overview of File Systems in Linux #
SUSE Linux Enterprise Server ships with different file systems from which to choose, including Btrfs, Ext4, Ext3, Ext2 and XFS. Each file system has its own advantages and disadvantages. For a side-by-side feature comparison of the major file systems in SUSE Linux Enterprise Server, see https://www.suse.com/releasenotes/x86_64/SUSE-SLES/15-SP2/#allArch-filesystems (File System Support and Sizes). This chapter contains an overview of how these file systems work and what advantages they offer.
With SUSE Linux Enterprise 12, Btrfs is the default file system for the operating system and XFS is the default for all other use cases. SUSE also continues to support the Ext family of file systems, and OCFS2. By default, the Btrfs file system will be set up with subvolumes. Snapshots will be automatically enabled for the root file system using the snapper infrastructure. For more information about snapper, refer to Book “Administration Guide”, Chapter 7 “System Recovery and Snapshot Management with Snapper”.
Professional high-performance setups might require a highly available storage system. To meet the requirements of high-performance clustering scenarios, SUSE Linux Enterprise Server includes OCFS2 (Oracle Cluster File System 2) and the Distributed Replicated Block Device (DRBD) in the High Availability add-on. These advanced storage systems are not covered in this guide. For information, see the Administration Guide for the SUSE Linux Enterprise High Availability.
It is very important to remember that no file system best suits all kinds of applications. Each file system has its particular strengths and weaknesses, which must be taken into account. In addition, even the most sophisticated file system cannot replace a reasonable backup strategy.
The terms data integrity and data consistency, when used in this section, do not refer to the consistency of the user space data (the data your application writes to its files). Whether this data is consistent must be controlled by the application itself.
Unless stated otherwise in this section, all the steps required to set up or change partitions and file systems can be performed by using the YaST Partitioner (which is also strongly recommended). For information, see Book “Deployment Guide”, Chapter 10 “Expert Partitioner”.
1.1 Terminology #
- metadata
A data structure that is internal to the file system. It ensures that all of the on-disk data is properly organized and accessible. Almost every file system has its own structure of metadata, which is one reason the file systems show different performance characteristics. It is extremely important to maintain metadata intact, because otherwise all data on the file system could become inaccessible.
- inode
A data structure on a file system that contains a variety of information about a file, including size, number of links, pointers to the disk blocks where the file contents are actually stored, and date and time of creation, modification, and access.
- journal
In the context of a file system, a journal is an on-disk structure containing a type of log in which the file system stores what it is about to change in the file system’s metadata. Journaling greatly reduces the recovery time of a file system because it has no need for the lengthy search process that checks the entire file system at system start-up. Instead, only the journal is replayed.
1.2 Btrfs #
Btrfs is a copy-on-write (COW) file system developed by Chris Mason. It is based on COW-friendly B-trees developed by Ohad Rodeh. Btrfs is a logging-style file system. Instead of journaling the block changes, it writes them in a new location, then links the change in. Until the last write, the new changes are not committed.
1.2.1 Key Features #
Btrfs provides fault tolerance, repair, and easy management features, such as the following:
Writable snapshots that allow you to easily roll back your system if needed after applying updates, or to back up files.
Subvolume support: Btrfs creates a default subvolume in its assigned pool of space. It allows you to create additional subvolumes that act as individual file systems within the same pool of space. The number of subvolumes is limited only by the space allocated to the pool.
The online check and repair functionality
scrub
is available as part of the Btrfs command line tools. It verifies the integrity of data and metadata, assuming the tree structure is fine. You can run scrub periodically on a mounted file system; it runs as a background process during normal operation.Different RAID levels for metadata and user data.
Different checksums for metadata and user data to improve error detection.
Integration with Linux Logical Volume Manager (LVM) storage objects.
Integration with the YaST Partitioner and AutoYaST on SUSE Linux Enterprise Server. This also includes creating a Btrfs file system on Multiple Devices (MD) and Device Mapper (DM) storage configurations.
Offline migration from existing Ext2, Ext3, and Ext4 file systems.
Boot loader support for
/boot
, allowing to boot from a Btrfs partition.Multivolume Btrfs is supported in RAID0, RAID1, and RAID10 profiles in SUSE Linux Enterprise Server 15 SP2. Higher RAID levels are not supported yet, but might be enabled with a future service pack.
Use Btrfs commands to set up transparent compression.
1.2.2 The Root File System Setup on SUSE Linux Enterprise Server #
By default, SUSE Linux Enterprise Server is set up using Btrfs and snapshots for the root partition. Snapshots allow you to easily roll back your system if needed after applying updates, or to back up files. Snapshots can easily be managed with the SUSE Snapper infrastructure as explained in Book “Administration Guide”, Chapter 7 “System Recovery and Snapshot Management with Snapper”. For general information about the SUSE Snapper project, see the Snapper Portal wiki at OpenSUSE.org (http://snapper.io).
When using a snapshot to roll back the system, it must be ensured that data such as user's home directories, Web and FTP server contents or log files do not get lost or overwritten during a roll back. This is achieved by using Btrfs subvolumes on the root file system. Subvolumes can be excluded from snapshots. The default root file system setup on SUSE Linux Enterprise Server as proposed by YaST during the installation contains the following subvolumes. They are excluded from snapshots for the reasons given below.
/boot/grub2/i386-pc
,/boot/grub2/x86_64-efi
,/boot/grub2/powerpc-ieee1275
,/boot/grub2/s390x-emu
A rollback of the boot loader configuration is not supported. The directories listed above are architecture-specific. The first two directories are present on AMD64/Intel 64 machines, the latter two on IBM POWER and on IBM Z, respectively.
/home
If
/home
does not reside on a separate partition, it is excluded to avoid data loss on rollbacks./opt
Third-party products usually get installed to
/opt
. It is excluded to avoid uninstalling these applications on rollbacks./srv
Contains data for Web and FTP servers. It is excluded to avoid data loss on rollbacks.
/tmp
All directories containing temporary files and caches are excluded from snapshots.
/usr/local
This directory is used when manually installing software. It is excluded to avoid uninstalling these installations on rollbacks.
/var
This directory contains many variable files, including logs, temporary caches, third party products in
/var/opt
, and is the default location for virtual machine images and databases. Therefore this subvolume is created to exclude all of this variable data from snapshots and has Copy-On-Write disabled.
Rollbacks are only supported by SUSE if you do not remove any of the preconfigured subvolumes. You may, however, add subvolumes using the YaST Partitioner.
1.2.2.1 Mounting Compressed Btrfs File Systems #
GRUB 2 cannot boot from lzo or zstd compressed root file systems. Use
zlib compression, or create a separate /boot
partition if you wish to use lzo or zstd compression for root.
The Btrfs file system supports transparent compression. While enabled, Btrfs compresses file data when written and uncompresses file data when read.
Use the compress
or compress-force
mount
option and select the compression algorithm, zstd
,
lzo
or zlib
(the default). zlib
compression has a higher compression ratio while lzo is faster and takes
less CPU load. The zstd algorithm offers a modern compromise, with
performance close to lzo and compression ratios similar to zlib.
For example:
#
mount -o compress=zstd /dev/sdx /mnt
In case you create a file, write to it, and the compressed result is
greater or equal to the uncompressed size, Btrfs will skip compression for
future write operations forever for this file. If you do not like this
behavior, use the compress-force
option. This can be
useful for files that have some initial non-compressible data.
Note, compression takes effect for new files only. Files that were written
without compression are not compressed when the file system is mounted
with the compress
or compress-force
option. Furthermore, files with the nodatacow
attribute
never get their extents compressed:
#
chattr
+C FILE#
mount
-o nodatacow /dev/sdx /mnt
In regard to encryption, this is independent from any compression. After you have written some data to this partition, print the details:
#
btrfs filesystem show /mnt
btrfs filesystem show /mnt
Label: 'Test-Btrfs' uuid: 62f0c378-e93e-4aa1-9532-93c6b780749d
Total devices 1 FS bytes used 3.22MiB
devid 1 size 2.00GiB used 240.62MiB path /dev/sdb1
If you want this to be permanent, add the compress
or
compress-force
option into the
/etc/fstab
configuration file. For example:
UUID=1a2b3c4d /home btrfs subvol=@/home,compress 0 0
1.2.2.2 Mounting Subvolumes #
A system rollback from a snapshot on SUSE Linux Enterprise Server is performed by booting from the snapshot first. This allows you to check the snapshot while running before doing the rollback. Being able to boot from snapshots is achieved by mounting the subvolumes (which would normally not be necessary).
In addition to the subvolumes listed in
Section 1.2.2, “The Root File System Setup on SUSE Linux Enterprise Server” a volume named
@
exists. This is the default subvolume that will be
mounted as the root partition (/
). The other
subvolumes will be mounted into this volume.
When booting from a snapshot, not the @
subvolume will
be used, but rather the snapshot. The parts of the file system included in
the snapshot will be mounted read-only as /
. The
other subvolumes will be mounted writable into the snapshot. This state is
temporary by default: the previous configuration will be restored with the
next reboot. To make it permanent, execute the snapper
rollback
command. This will make the snapshot that is currently
booted the new default subvolume, which will be used
after a reboot.
1.2.2.3 Checking for Free Space #
File system usage is usually checked by running the df
command. On a Btrfs file system, the output of df
can
be misleading, because in addition to the space the raw data allocates, a
Btrfs file system also allocates and uses space for metadata.
Consequently a Btrfs file system may report being out of space even though it seems that plenty of space is still available. In that case, all space allocated for the metadata is used up. Use the following commands to check for used and available space on a Btrfs file system:
btrfs filesystem show
>
sudo
btrfs filesystem show / Label: 'ROOT' uuid: 52011c5e-5711-42d8-8c50-718a005ec4b3 Total devices 1 FS bytes used 10.02GiB devid 1 size 20.02GiB used 13.78GiB path /dev/sda3Shows the total size of the file system and its usage. If these two values in the last line match, all space on the file system has been allocated.
btrfs filesystem df
>
sudo
btrfs filesystem df / Data, single: total=13.00GiB, used=9.61GiB System, single: total=32.00MiB, used=16.00KiB Metadata, single: total=768.00MiB, used=421.36MiB GlobalReserve, single: total=144.00MiB, used=0.00BShows values for allocated (
total
) and used space of the file system. If the values fortotal
andused
for the metadata are almost equal, all space for metadata has been allocated.btrfs filesystem usage
>
sudo
btrfs filesystem usage / Overall: Device size: 20.02GiB Device allocated: 13.78GiB Device unallocated: 6.24GiB Device missing: 0.00B Used: 10.02GiB Free (estimated): 9.63GiB (min: 9.63GiB) Data ratio: 1.00 Metadata ratio: 1.00 Global reserve: 144.00MiB (used: 0.00B) Data Metadata System Id Path single single single Unallocated -- --------- -------- --------- -------- ----------- 1 /dev/sda3 13.00GiB 768.00MiB 32.00MiB 6.24GiB -- --------- -------- --------- -------- ----------- Total 13.00GiB 768.00MiB 32.00MiB 6.24GiB Used 9.61GiB 421.36MiB 16.00KiBShows data similar to that of the two previous commands combined.
For more information refer to man 8 btrfs-filesystem
and https://btrfs.wiki.kernel.org/index.php/FAQ.
1.2.3 Migration from ReiserFS and Ext File Systems to Btrfs #
You can migrate data volumes from existing ReiserFS or Ext (Ext2, Ext3, or
Ext4) to the Btrfs file system using the btrfs-convert
tool. This allows you to do an in-place conversion of unmounted (offline)
file systems, which may require a bootable install media with the
btrfs-convert
tool. The tool constructs a Btrfs file
system within the free space of the original file system, directly linking
to the data contained in it. There must be enough free space on the device
to create the metadata or the conversion will fail. The original file
system will be intact and no free space will be occupied by the Btrfs file
system. The amount of space required is dependent on the content of the
file system and can vary based on the number of file system objects (such
as files, directories, extended attributes) contained in it. Since the data
is directly referenced, the amount of data on the file system does not
impact the space required for conversion, except for files that use tail
packing and are larger than about 2 KiB in size.
Converting the root file system to Btrfs is not supported and not
recommended. Automating such a conversion is not possible due to various
steps that need to be tailored to your specific setup—the process
requires a complex configuration to provide a correct rollback,
/boot
must be on the root file system, and the system
must have specific subvolumes, etc. Either keep the existing file system
or re-install the whole system from scratch.
To convert the original file system to the Btrfs file system, run:
#
btrfs-convert /path/to/device
/etc/fstab
After the conversion, you need to ensure that any references to the
original file system in /etc/fstab
have been adjusted
to indicate that the device contains a Btrfs file system.
When converted, the contents of the Btrfs file system will reflect the
contents of the source file system. The source file system will be
preserved until you remove the related read-only image created at
fs_root/reiserfs_saved/image
.
The image file is effectively a 'snapshot' of the ReiserFS file system
prior to conversion and will not be modified as the Btrfs file system is
modified. To remove the image file, remove the
reiserfs_saved
subvolume:
#
btrfs subvolume delete fs_root/reiserfs_saved
To revert the file system back to the original one, use the following command:
#
btrfs-convert -r /path/to/device
Any changes you made to the file system while it was mounted as a Btrfs file system will be lost. A balance operation must not have been performed in the interim, or the file system will not be restored correctly.
1.2.4 Btrfs Administration #
Btrfs is integrated in the YaST Partitioner and AutoYaST. It is available during the installation to allow you to set up a solution for the root file system. You can use the YaST Partitioner after the installation to view and manage Btrfs volumes.
Btrfs administration tools are provided in the
btrfsprogs
package. For information about using Btrfs
commands, see the man 8 btrfs
, man 8
btrfsck
, and man 8 mkfs.btrfs
commands. For
information about Btrfs features, see the Btrfs wiki
at http://btrfs.wiki.kernel.org.
1.2.5 Btrfs Quota Support for Subvolumes #
The Btrfs root file system subvolumes (for example,
/var/log
, /var/crash
, or
/var/cache
) can use all the available disk space
during normal operation, and cause a system malfunction. To help avoid this
situation, SUSE Linux Enterprise Server offers quota support for Btrfs subvolumes. If you
set up the root file system from a YaST proposal, you are ready to enable
and set subvolume quotas.
Enable quota support:
>
sudo
btrfs quota enable /Get a list of subvolumes:
>
sudo
btrfs subvolume list /Quotas can only be set for existing subvolumes.
Set a quota for one of the subvolumes that was listed in the previous step. A subvolume can either be identified by path (for example
/var/tmp
) or by0/SUBVOLUME ID
(for example0/272
). The following example sets a quota of 5 GB for/var/tmp
.>
sudo
btrfs qgroup limit 5G /var/tmpThe size can either be specified in bytes (5000000000), kilobytes (5000000K), megabytes (5000M), or gigabytes (5G). The resulting values in bytes slightly differ, since 1024 Bytes = 1 KiB, 1024 KiB = 1 MiB, etc.
To list the existing quotas, use the following command. The column
max_rfer
shows the quota in bytes.>
sudo
btrfs qgroup show -r /
In case you want to nullify an existing quota, set a quota size of
none
:
>
sudo
btrfs qgroup limit none /var/tmp
To disable quota support for a partition and all its subvolumes, use
btrfs quota disable
:
>
sudo
btrfs quota disable /
See the man 8 btrfs-qgroup
and man 8
btrfs-quota
for more details. The UseCases
page on the Btrfs wiki
(https://btrfs.wiki.kernel.org/index.php/UseCases)
also provides more information.
1.2.6 Swapping on Btrfs #
You will not be able to create a snapshot if there is any enabled swap file in the source subvolume.
SLES supports swapping to a file on the btrfs filesystem if the following criteria relating to the resulting swap file are fulfilled:
the swap file must have the
NODATACOW
andNODATASUM
mount options.the swap file can not be compressed—that you can acomplish by setting the
NODATACOW
andNODATASUM
mount options. Both options disable the swap file compression.the swap file can not be activated while exclusive operations are running—such as device resizing, adding, removing or replacing or when a balancing operation is running.
The swap file can not be sparse.
The swap file can not be an inline file.
The swap file must be on a
single
allocation profile filesystem.
1.2.7 Btrfs send/receive #
Btrfs allows to make snapshots to capture the state of the file system. Snapper, for example, uses this feature to create snapshots before and after system changes, allowing a rollback. However, together with the send/receive feature, snapshots can also be used to create and maintain copies of a file system in a remote location. This feature can, for example, be used to do incremental backups.
A btrfs send
operation calculates the difference between
two read-only snapshots from the same subvolume and sends it to a file or
to STDOUT. A btrfs receive
operation takes the result of
the send command and applies it to a snapshot.
1.2.7.1 Prerequisites #
To use the send/receive feature, the following requirements need to be met:
A Btrfs file system is required on the source side (
send
) and on the target side (receive
).Btrfs send/receive operates on snapshots, therefore the respective data needs to reside in a Btrfs subvolume.
Snapshots on the source side need to be read-only.
SUSE Linux Enterprise 12 SP2 or better. Earlier versions of SUSE Linux Enterprise do not support send/receive.
1.2.7.2 Incremental Backups #
The following procedure shows the basic usage of Btrfs send/receive using
the example of creating incremental backups of /data
(source side) in /backup/data
(target side).
/data
needs to be a subvolume.
Create the initial snapshot (called
snapshot_0
in this example) on the source side and make sure it is written to the disk:>
sudo
btrfs subvolume snapshot -r /data /data/bkp_data syncA new subvolume
/data/bkp_data
is created. It will be used as the basis for the next incremental backup and should be kept as a reference.Send the initial snapshot to the target side. Since this is the initial send/receive operation, the complete snapshot needs to be sent:
>
sudo
bash -c 'btrfs send /data/bkp_data | btrfs receive /backup'A new subvolume
/backup/bkp_data
is created on the target side.
When the initial setup has been finished, you can create incremental backups and send the differences between the current and previous snapshots to the target side. The procedure is always the same:
Create a new snapshot on the source side.
Send the differences to the target side.
Optional: Rename and/or clean up snapshots on both sides.
Create a new snapshot on the source side and make sure it is written to the disk. In the following example the snapshot is named bkp_data_CURRENT_DATE:
>
sudo
btrfs subvolume snapshot -r /data /data/bkp_data_$(date +%F) syncA new subvolume, for example
/data/bkp_data_2016-07-07
, is created.Send the difference between the previous snapshot and the one you have created to the target side. This is achieved by specifying the previous snapshot with the option
-p SNAPSHOT
.>
sudo
bash -c 'btrfs send -p /data/bkp_data /data/bkp_data_2016-07-07 \ | btrfs receive /backup'A new subvolume
/backup/bkp_data_2016-07-07
is created.As a result four snapshots, two on each side, exist:
/data/bkp_data
/data/bkp_data_2016-07-07
/backup/bkp_data
/backup/bkp_data_2016-07-07
Now you have three options for how to proceed:
Keep all snapshots on both sides. With this option you can roll back to any snapshot on both sides while having all data duplicated at the same time. No further action is required. When doing the next incremental backup, keep in mind to use the next-to-last snapshot as parent for the send operation.
Only keep the last snapshot on the source side and all snapshots on the target side. Also allows to roll back to any snapshot on both sides—to do a rollback to a specific snapshot on the source side, perform a send/receive operation of a complete snapshot from the target side to the source side. Do a delete/move operation on the source side.
Only keep the last snapshot on both sides. This way you have a backup on the target side that represents the state of the last snapshot made on the source side. It is not possible to roll back to other snapshots. Do a delete/move operation on the source and the target side.
To only keep the last snapshot on the source side, perform the following commands:
>
sudo
btrfs subvolume delete /data/bkp_data>
sudo
mv /data/bkp_data_2016-07-07 /data/bkp_dataThe first command will delete the previous snapshot, the second command renames the current snapshot to
/data/bkp_data
. This ensures that the last snapshot that was backed up is always named/data/bkp_data
. As a consequence, you can also always use this subvolume name as a parent for the incremental send operation.To only keep the last snapshot on the target side, perform the following commands:
>
sudo
btrfs subvolume delete /backup/bkp_data>
sudo
mv /backup/bkp_data_2016-07-07 /backup/bkp_dataThe first command will delete the previous backup snapshot, the second command renames the current backup snapshot to
/backup/bkp_data
. This ensures that the latest backup snapshot is always named/backup/bkp_data
.
To send the snapshots to a remote machine, use SSH:
>
btrfs send /data/bkp_data | ssh root@jupiter.example.com 'btrfs receive /backup'
1.2.8 Data Deduplication Support #
Btrfs supports data deduplication by replacing identical blocks in the file
system with logical links to a single copy of the block in a common storage
location. SUSE Linux Enterprise Server provides the tool duperemove
for
scanning the file system for identical blocks. When used on a Btrfs file
system, it can also be used to deduplicate these blocks and thus save space
on the file system. duperemove
is not installed by
default. To make it available, install the package
duperemove .
If you intend to deduplicate a large amount of files, use the
--hashfile
option:
>
sudo
duperemove--hashfile HASH_FILE
file1 file2 file3
The --hashfile
option stores hashes of all specified
files into the HASH_FILE instead of RAM and
prevents it from being exhausted. HASH_FILE is
reusable—you can deduplicate changes to large datasets very quickly
after an initial run that generated a baseline hash file.
duperemove
can either operate on a list of files or
recursively scan a directory:
>
sudo
duperemove OPTIONS file1 file2 file3>
sudo
duperemove -r OPTIONS directory
It operates in two modes: read-only and de-duping. When run in read-only
mode (that is without the -d
switch), it scans the given
files or directories for duplicated blocks and prints them. This works on
any file system.
Running duperemove
in de-duping mode is only supported
on Btrfs file systems. After having scanned the given files or directories,
the duplicated blocks will be submitted for deduplication.
For more information see man 8 duperemove
.
1.2.9 Deleting Subvolumes from the Root File System #
You may need to delete one of the default Btrfs subvolumes from the root
file system for specific purposes. One of them is transforming a
subvolume—for example @/home
or
@/srv
—into a file system on a separate device.
The following procedure illustrates how to delete a Btrfs subvolume:
Identify the subvolume you need to delete (for example
@/opt
). Notice that the root path has always subvolume ID '5'.>
sudo
btrfs subvolume list / ID 256 gen 30 top level 5 path @ ID 258 gen 887 top level 256 path @/var ID 259 gen 872 top level 256 path @/usr/local ID 260 gen 886 top level 256 path @/tmp ID 261 gen 60 top level 256 path @/srv ID 262 gen 886 top level 256 path @/root ID 263 gen 39 top level 256 path @/opt [...]Find the device name that hosts the root partition:
>
sudo
btrfs device usage / /dev/sda1, ID: 1 Device size: 23.00GiB Device slack: 0.00B Data,single: 7.01GiB Metadata,DUP: 1.00GiB System,DUP: 16.00MiB Unallocated: 14.98GiBMount the root file system (subvolume with ID 5) on a separate mount point (for example
/mnt
):>
sudo
mount -o subvolid=5 /dev/sda1 /mntDelete the
@/opt
partition from the mounted root file system:>
sudo
btrfs subvolume delete /mnt/@/optUnmount the previously mounted root file system:
>
sudo
umount /mnt
1.3 XFS #
Originally intended as the file system for their IRIX OS, SGI started XFS development in the early 1990s. The idea behind XFS was to create a high-performance 64-bit journaling file system to meet extreme computing challenges. XFS is very good at manipulating large files and performs well on high-end hardware. XFS is the default file system for data partitions in SUSE Linux Enterprise Server.
A quick review of XFS’s key features explains why it might prove to be a strong competitor for other journaling file systems in high-end computing.
- High scalability
XFS offers high scalability by using allocation groups
At the creation time of an XFS file system, the block device underlying the file system is divided into eight or more linear regions of equal size. Those are called allocation groups. Each allocation group manages its own inodes and free disk space. Practically, allocation groups can be seen as file systems in a file system. Because allocation groups are rather independent of each other, more than one of them can be addressed by the kernel simultaneously. This feature is the key to XFS’s great scalability. Naturally, the concept of independent allocation groups suits the needs of multiprocessor systems.
- High performance
XFS offers high performance through efficient management of disk space
Free space and inodes are handled by B+ trees inside the allocation groups. The use of B+ trees greatly contributes to XFS’s performance and scalability. XFS uses delayed allocation, which handles allocation by breaking the process into two pieces. A pending transaction is stored in RAM and the appropriate amount of space is reserved. XFS still does not decide where exactly (in file system blocks) the data should be stored. This decision is delayed until the last possible moment. Some short-lived temporary data might never make its way to disk, because it is obsolete by the time XFS decides where to save it. In this way, XFS increases write performance and reduces file system fragmentation. Because delayed allocation results in less frequent write events than in other file systems, it is likely that data loss after a crash during a write is more severe.
- Preallocation to avoid file system fragmentation
Before writing the data to the file system, XFS reserves (preallocates) the free space needed for a file. Thus, file system fragmentation is greatly reduced. Performance is increased because the contents of a file are not distributed all over the file system.
1.3.1 XFS formats #
SUSE Linux Enterprise Server supports the “on-disk format” (v5) of the XFS file system. The main advantages of this format are automatic checksums of all XFS metadata, file type support, and support for a larger number of access control lists for a file.
Note that this format is not supported by SUSE Linux Enterprise
kernels older than version 3.12, by xfsprogs
older than version 3.2.0, and
GRUB 2 versions released before SUSE Linux Enterprise 12.
XFS is deprecating file systems with the V4 format. This file system format was created by the command:
mkfs.xfs -m crc=0 DEVICE
The format was used in SLE 11 and older releases and currently it creates a warning message by dmesg
:
Deprecated V4 format (crc=0) will not be supported after September 2030
If you see the message above in the output of the dmesg
command, it is recommended that you update your file system to the V5 format:
Back up your data to another device.
Create the file system on the device.
mkfs.xfs -m crc=1 DEVICE
Restore the data from the backup on the updated device.
1.4 Ext2 #
The origins of Ext2 go back to the early days of Linux history. Its predecessor, the Extended File System, was implemented in April 1992 and integrated in Linux 0.96c. The Extended File System underwent several modifications and, as Ext2, became the most popular Linux file system for years. With the creation of journaling file systems and their short recovery times, Ext2 became less important.
A brief summary of Ext2’s strengths might help understand why it was—and in some areas still is—the favorite Linux file system of many Linux users.
- Solidity and Speed
Being an “old-timer”, Ext2 underwent many improvements and was heavily tested. This might be the reason people often refer to it as rock-solid. After a system outage when the file system could not be cleanly unmounted, e2fsck starts to analyze the file system data. Metadata is brought into a consistent state and pending files or data blocks are written to a designated directory (called
lost+found
). In contrast to journaling file systems, e2fsck analyzes the entire file system and not only the recently modified bits of metadata. This takes significantly longer than checking the log data of a journaling file system. Depending on file system size, this procedure can take half an hour or more. Therefore, it is not desirable to choose Ext2 for any server that needs high availability. However, because Ext2 does not maintain a journal and uses less memory, it is sometimes faster than other file systems.- Easy Upgradability
Because Ext3 is based on the Ext2 code and shares its on-disk format and its metadata format, upgrades from Ext2 to Ext3 are very easy.
1.5 Ext3 #
Ext3 was designed by Stephen Tweedie. Unlike all other next-generation file systems, Ext3 does not follow a completely new design principle. It is based on Ext2. These two file systems are very closely related to each other. An Ext3 file system can be easily built on top of an Ext2 file system. The most important difference between Ext2 and Ext3 is that Ext3 supports journaling. In summary, Ext3 has three major advantages to offer:
1.5.1 Easy and Highly Reliable Upgrades from Ext2 #
The code for Ext2 is the strong foundation on which Ext3 could become a highly acclaimed next-generation file system. Its reliability and solidity are elegantly combined in Ext3 with the advantages of a journaling file system. Unlike transitions to other journaling file systems, such as XFS, which can be quite tedious (making backups of the entire file system and re-creating it from scratch), a transition to Ext3 is a matter of minutes. It is also very safe, because re-creating an entire file system from scratch might not work flawlessly. Considering the number of existing Ext2 systems that await an upgrade to a journaling file system, you can easily see why Ext3 might be of some importance to many system administrators. Downgrading from Ext3 to Ext2 is as easy as the upgrade. Perform a clean unmount of the Ext3 file system and remount it as an Ext2 file system.
1.5.2 Converting an Ext2 File System into Ext3 #
To convert an Ext2 file system to Ext3:
Create an Ext3 journal by running
tune2fs -j
as theroot
user.This creates an Ext3 journal with the default parameters.
To specify how large the journal should be and on which device it should reside, run
tune2fs
-J
instead together with the desired journal optionssize=
anddevice=
. More information about thetune2fs
program is available in thetune2fs
man page.Edit the file
/etc/fstab
as theroot
user to change the file system type specified for the corresponding partition fromext2
toext3
, then save the changes.This ensures that the Ext3 file system is recognized as such. The change takes effect after the next reboot.
To boot a root file system that is set up as an Ext3 partition, add the modules
ext3
andjbd
in theinitrd
. Do so byopening or creating
/etc/dracut.conf.d/filesystem.conf
and adding the following line (mind the leading blank space):force_drivers+=" ext3 jbd"
and running the
dracut
-f
command.
Reboot the system.
1.6 Ext4 #
In 2006, Ext4 started as a fork from Ext3. It is the latest file system in the extended file system version. Ext4 was originally designed to increase storage size by supporting volumes with a size of up to 1 exbibyte, files with a size of up to 16 tebibytes and an unlimited number of subdirectories. Ext4 uses extents, instead of the traditional direct and indirect block pointers, to map the file contents. Usage of extents improves both storage and retrieval of data from disks.
Ext4 also introduces several performance enhancements such as delayed block allocation and a much faster file system checking routine. Ext4 is also more reliable by supporting journal checksums and by providing time stamps measured in nanoseconds. Ext4 is fully backward compatible to Ext2 and Ext3—both file systems can be mounted as Ext4.
The Ext3 funcionality is fully supported by the Ext4 driver in the Ext4 kernel module.
1.6.1 Reliability and performance #
Some other journaling file systems follow the “metadata-only”
journaling approach. This means your metadata is always kept in a
consistent state, but this cannot be automatically guaranteed for the file
system data itself. Ext4 is designed to take care of both metadata and
data. The degree of “care” can be customized. Mounting Ext4 in
the data=journal
mode offers maximum security (data
integrity), but can slow down the system because both metadata and data are
journaled. Another approach is to use the
data=ordered
mode, which ensures both data and metadata
integrity, but uses journaling only for metadata. The file system driver
collects all data blocks that correspond to one metadata update. These data
blocks are written to disk before the metadata is updated. As a result,
consistency is achieved for metadata and data without sacrificing
performance. A third mount option to use is data=writeback
,
which allows data to be written to the main file system after its metadata
has been committed to the journal. This option is often considered the best
in performance. It can, however, allow old data to reappear in files after
crash and recovery while internal file system integrity is maintained. Ext4
uses the data=ordered
option as the default.
1.6.2 Ext4 file system inode size and number of inodes #
An inode stores information about the file and its block location in the file system. To allow space in the inode for extended attributes and ACLs, the default inode size was increased to 256 bytes.
When you create a new Ext4 file system, the space in the inode table is preallocated for the total number of inodes that can be created. The bytes-per-inode ratio and the size of the file system determine how many inodes are possible. When the file system is made, an inode is created for every bytes-per-inode bytes of space:
number of inodes = total size of the file system divided by the number of bytes per inode
The number of inodes controls the number of files you can have in the file system: one inode for each file.
After the inodes are allocated, you cannot change the settings for the inode size or bytes-per-inode ratio. No new inodes are possible without re-creating the file system with different settings, or unless the file system gets extended. When you exceed the maximum number of inodes, no new files can be created on the file system until some files are deleted.
When you make a new Ext4 file system, you can specify the inode size and
bytes-per-inode ratio to control inode space usage and the number of files
possible on the file system. If the blocks size, inode size, and
bytes-per-inode ratio values are not specified, the default values in the
/etc/mked2fs.conf
file are applied. For information,
see the mke2fs.conf(5)
man page.
Use the following guidelines:
Inode size: The default inode size is 256 bytes. Specify a value in bytes that is a power of 2 and equal to 128 or larger in bytes and up to the block size, such as 128, 256, 512, and so on. Use 128 bytes only if you do not use extended attributes or ACLs on your Ext4 file systems.
Bytes-per-inode ratio: The default bytes-per-inode ratio is 16384 bytes. Valid bytes-per-inode ratio values must be a power of 2 equal to 1024 or greater in bytes, such as 1024, 2048, 4096, 8192, 16384, 32768, and so on. This value should not be smaller than the block size of the file system, because the block size is the smallest chunk of space used to store data. The default block size for the Ext4 file system is 4 KiB.
In addition, consider the number of files and the size of files you need to store. For example, if your file system will have many small files, you can specify a smaller bytes-per-inode ratio, which increases the number of inodes. If your file system will have very large files, you can specify a larger bytes-per-inode ratio, which reduces the number of possible inodes.
Generally, it is better to have too many inodes than to run out of them. If you have too few inodes and very small files, you could reach the maximum number of files on a disk that is practically empty. If you have too many inodes and very large files, you might have free space reported but be unable to use it because you cannot create new files in space reserved for inodes.
Use any of the following methods to set the inode size and bytes-per-inode ratio:
Modifying the default settings for all new ext4 file systems: In a text editor, modify the
defaults
section of the/etc/mke2fs.conf
file to set theinode_size
andinode_ratio
to the desired default values. The values apply to all new Ext4 file systems. For example:blocksize = 4096 inode_size = 128 inode_ratio = 8192
At the command line: Pass the inode size (
-I 128
) and the bytes-per-inode ratio (-i 8192
) to themkfs.ext4(8)
command or themke2fs(8)
command when you create a new ext4 file system. For example, use either of the following commands:>
sudo
mkfs.ext4 -b 4096 -i 8092 -I 128 /dev/sda2>
sudo
mke2fs -t ext4 -b 4096 -i 8192 -I 128 /dev/sda2During installation with YaST: Pass the inode size and bytes-per-inode ratio values when you create a new Ext4 file system during the installation. In the , select the partition, click . Under , select , then click . In the dialog, select the desired values from the , , and drop-down box.
For example, select 4096 for the
drop-down box, select 8192 from the drop-down box, select 128 from the drop-down box, then click .
1.6.3 Upgrading to Ext4 #
Back up all data on the file system before performing any update of your file system.
To upgrade from Ext2 or Ext3, you must enable the following:
Features required by Ext4 #- extents
contiguous blocks on the hard disk that are used to keep files close together and prevent fragmentation
- unint_bg
lazy inode table initialization
- dir_index
hashed b-tree lookups for large directores
- on Ext2:
as_journal
enable journalling on your Ext2 file system.
To enable the features, run:
on Ext3:
#
tune2fs -O extents,uninit_bg,dir_index DEVICE_NAMEon Ext2:
#
tune2fs -O extents,uninit_bg,dir_index,has_journal DEVICE_NAME
As
root
edit the/etc/fstab
file: change theext3
orext2
record toext4
. The change takes effect after the next reboot.To boot a file system that is setup on an ext4 parition, add the modules:
ext4
andjbd
in theinitramfs
. Open or create/etc/dracut.conf.d/filesystem.conf
and add the following line:force_drivers+=" ext4 jbd"
You need to overwrite the existing dracut
initramfs
by running:dracut -f
Reboot your system.
1.7 ReiserFS #
ReiserFS support was completely removed with SUSE Linux Enterprise Server 15. To migrate your existing partitions to Btrfs, refer to Section 1.2.3, “Migration from ReiserFS and Ext File Systems to Btrfs”.
1.8 tmpfs #
tmpfs is a RAM-based virtual memory file system. The file system is temporary, which means no files are stored on the hard disk, and when the file system is unmounted, all data is discarded.```
Data in this file system is stored in the kernel internal cache. The needed kernel cache space can grow or shrink.
The file system has the following characteristics:
Very fast access to files.
When swap is enabled for the tmpfs mount, unused data is swapped.
You can change the file system size during the
mount -o remount
operation without losing data. However, you cannot resize to the value lower than its current usage.tmpfs supports Transparent HugePage Support (THP).
For more information, you can refer to:
man tmpfs
1.9 Other Supported File Systems #
Table 1.1, “File System Types in Linux” summarizes some other file systems supported by Linux. They are supported mainly to ensure compatibility and interchange of data with different kinds of media or foreign operating systems.
File System Type |
Description |
---|---|
|
Standard file system on CD-ROMs. |
|
|
|
Network File System: Here, data can be stored on any machine in a network and access might be granted via a network. |
|
Windows NT file system; read-only. |
|
Server Message Block is used by products such as Windows to enable file access over a network. |
|
Used by BSD, SunOS, and NextStep. Only supported in read-only mode. |
|
Unix on MS-DOS: Applied on top of a standard |
|
Virtual FAT: Extension of the |
|
Extensible File Allocation Table. File system optimized for use with flash memory, such as USB flash drives and SD cards. |
1.10 Blacklisted file systems #
Due to security reasons, some file systems have been blacklisted. These file systems are usually not maintained anymore and are not in common use. However, the kernel module for a blacklisted file system can be loaded, because the in-kernel API is still compatible. A combination of user-mountable file systems and the automatic mounting of file systems on removable devices could result in the situation where unprivileged users might trigger the automatic loading of kernel modules, and the removable devices could store potentially malicious data.
To get a list of currently blacklisted file systems, run the following command:
>
sudo
rpm -ql suse-module-tools | sed -nE 's/.*blacklist_fs-(.*)\.conf/\1/p'
If you try to mount a device with a blacklisted file system using the
mount
command, the command outputs an error message, for
example:
mount: /mnt/mx: unknown filesystem type 'minix' (hint: possibly blacklisted, see mount(8)).
Even though a file system is blacklisted, you can load the corresponding
kernel module for the file system directly using
modprobe
:
>
sudo
modprobe FILESYSTEM
For example, for the cramfs
file system, the output looks as follows:
unblacklist: loading cramfs file system module unblacklist: Do you want to un-blacklist cramfs permanently (<y>es/<n>o/n<e>ver)? y unblacklist: cramfs un-blacklisted by creating /etc/modprobe.d/60-blacklist_fs-cramfs.conf
Here you have the following options:
- yes
The module will be loaded and removed from the blacklist. Therefore, the module will be loaded automatically in future without any other prompt.
The configuration file
/etc/modprobe.d/60-blacklist_fs-${MODULE}.conf
is created. Remove the file to undo the changes you performed.- no
The module will be loaded, but it is not removed from the blacklist. Therefore, on a next module loading you will see the prompt above again.
- ever
The module will be loaded, but autoloading is disabled even for future use, and the prompt will no longer be displayed.
The configuration file
/etc/modprobe.d/60-blacklist_fs-${MODULE}.conf
is created. Remove the file to undo the changes you performed.- Ctrl–c
This option is used to interrupt the module loading.
1.11 Large File Support in Linux #
Originally, Linux supported a maximum file size of 2 GiB (231 bytes). Unless a file system comes with large file support, the maximum file size on a 32-bit system is 2 GiB.
Currently, all our standard file systems have LFS (large file support), which gives a maximum file size of 263 bytes in theory. Table 1.2, “Maximum Sizes of Files and File Systems (On-Disk Format, 4 KiB Block Size)” offers an overview of the current on-disk format limitations of Linux files and file systems. The numbers in the table assume that the file systems are using 4 KiB block size, which is a common standard. When using different block sizes, the results are different. The maximum file sizes in Table 1.2, “Maximum Sizes of Files and File Systems (On-Disk Format, 4 KiB Block Size)” can be larger than the file system's actual size when using sparse blocks.
In this document: 1024 Bytes = 1 KiB; 1024 KiB = 1 MiB; 1024 MiB = 1 GiB; 1024 GiB = 1 TiB; 1024 TiB = 1 PiB; 1024 PiB = 1 EiB (see also NIST: Prefixes for Binary Multiples.
File System (4 KiB Block Size) |
Maximum File System Size |
Maximum File Size |
---|---|---|
Btrfs |
16 EiB |
16 EiB |
Ext3 |
16 TiB |
2 TiB |
Ext4 |
1 EiB |
16 TiB |
OCFS2 (a cluster-aware file system available in SLE HA) |
16 TiB |
1 EiB |
XFS |
16 EiB |
8 EiB |
NFSv2 (client side) |
8 EiB |
2 GiB |
NFSv3/NFSv4 (client side) |
8 EiB |
8 EiB |
Table 1.2, “Maximum Sizes of Files and File Systems (On-Disk Format, 4 KiB Block Size)” describes the limitations regarding the on-disk format. The Linux kernel imposes its own limits on the size of files and file systems handled by it. These are as follows:
- File Size
On 32-bit systems, files cannot exceed 2 TiB (241 bytes).
- File System Size
File systems can be up to 273 bytes in size. However, this limit is still out of reach for the currently available hardware.
1.12 Linux Kernel Storage Limitations #
Table 1.3, “Storage Limitations” summarizes the kernel limits for storage associated with SUSE Linux Enterprise Server.
Storage Feature |
Limitation |
---|---|
Maximum number of LUNs supported |
16384 LUNs per target. |
Maximum number of paths per single LUN |
No limit by default. Each path is treated as a normal LUN. The actual limit is given by the number of LUNs per target and the number of targets per HBA (16777215 for a Fibre Channel HBA). |
Maximum number of HBAs |
Unlimited. The actual limit is determined by the amount of PCI slots of the system. |
Maximum number of paths with device-mapper-multipath (in total) per operating system |
Approximately 1024. The actual number depends on the length of the device number strings for each multipath device. It is a compile-time variable within multipath-tools, which can be raised if this limit poses a problem. |
Maximum size per block device |
Up to 8 EiB. |
1.13 Freeing unused file system blocks #
On solid-state drives (SSDs) and thinly provisioned volumes, it is useful to
trim blocks that are not in use by the file system. SUSE Linux Enterprise Server fully
supports unmap
and TRIM
operations on
all file systems supporting them.
There are two types of commonly used TRIM—online
TRIM
and periodic TRIM
. The most
suitable way of trimming devices depends on your use case. In general, it is
recommended to use periodic TRIM, especially if the device has enough free
blocks. If the device is often near its full capacity, online TRIM is
preferable.
TRIM
support on devices
Always verify that your device supports the TRIM
operation before you attempt to use it. Otherwise, you might lose your data
on that device. To verify the TRIM
support, run the
command:
>
sudo
lsblk --discard
The command outputs information about all available block devices. If the
values of the columns DISC-GRAN
and
DISC-MAX
are non-zero, the device supports the
TRIM
operation.
1.13.1 Periodic TRIM #
Periodic TRIM is handled by the fstrim
command invoked
by systemd
on a regular basis. You can also run the command manually.
To schedule periodic TRIM, enable the fstrim.timer
as
follows:
>
sudo
systemctl enable fstrim.timer
systemd
creates a unit file in
/usr/lib/systemd/system
. By default, the service runs
once a week, which is usually sufficient. However, you can change the
frequency by configuring the OnCalendar
option to a
required value.
The default behaviour of fstrim
is to discard all blocks
in the file system. You can use options when invoking the command to modify
this behaviour. For example, you can pass the offset
option to define the place where to start the trimming procedure. For
details, see man fstrim
.
The fstrim
command can perform trimming on all devices
stored in the /etc/fstab
file, which support the
TRIM
operation—use the -A
option when invoking the command for this purpose.
1.13.2 Online TRIM #
Online TRIM of a device is performed each time data is written to the device.
To enable online TRIM on a device, add the discard
option to the /etc/fstab
file as follows:
UID=83df497d-bd6d-48a3-9275-37c0e3c8dc74 / btrfs defaults,discard
Alternatively, on the Ext4 file system you can use the
tune2fs
command to set the discard
option in /etc/fstab
:
>
sudo
tune2fs -o discard DEVICE
The discard
option is also added to
/etc/fstab
in case the device was mounted by
mount
with the discard
option:
>
sudo
mount -o discard DEVICE
Using the discard
option may decrease the lifetime of some
lower-quality SSD devices. Online TRIM can also impact the performance of
the device, for example, if a larger amount of data is deleted. In this
situation, an erase block might be reallocated, and shortly afterwards,
the same erase block might be marked as unused again.
1.14 Troubleshooting File Systems #
This section describes some known issues and possible solutions for file systems.
1.14.1 Btrfs Error: No space is left on device #
The root (/
) partition using the Btrfs file system
stops accepting data. You receive the error “No space left
on device
”.
See the following sections for information about possible causes and prevention of this issue.
1.14.1.1 Disk Space Consumed by Snapper Snapshots #
If Snapper is running for the Btrfs file system, the “No
space left on device
” problem is typically caused by
having too much data stored as snapshots on your system.
You can remove some snapshots from Snapper, however, the snapshots are not deleted immediately and might not free up as much space as you need.
To delete files from Snapper:
Open a terminal.
At the command prompt, enter
btrfs filesystem show
, for example:>
sudo
btrfs filesystem show Label: none uuid: 40123456-cb2c-4678-8b3d-d014d1c78c78 Total devices 1 FS bytes used 20.00GB devid 1 size 20.00GB used 20.00GB path /dev/sda3Enter
>
sudo
btrfs fi balance start MOUNTPOINT -dusage=5This command attempts to relocate data in empty or near-empty data chunks, allowing the space to be reclaimed and reassigned to metadata. This can take a while (many hours for 1 TB) although the system is otherwise usable during this time.
List the snapshots in Snapper. Enter
>
sudo
snapper -c root listDelete one or more snapshots from Snapper. Enter
>
sudo
snapper -c root delete SNAPSHOT_NUMBER(S)Ensure that you delete the oldest snapshots first. The older a snapshot is, the more disk space it occupies.
To help prevent this problem, you can change the Snapper cleanup
algorithms. See Book “Administration Guide”, Chapter 7 “System Recovery and Snapshot Management with Snapper”, Section 7.6.1.2 “Cleanup Algorithms” for
details. The configuration values controlling snapshot cleanup are
EMPTY_*
, NUMBER_*
, and
TIMELINE_*
.
If you use Snapper with Btrfs on the file system disk, it is advisable to reserve twice the amount of disk space than the standard storage proposal. The YaST Partitioner automatically proposes twice the standard disk space in the Btrfs storage proposal for the root file system.
1.14.1.2 Disk Space Consumed by Log, Crash, and Cache Files #
If the system disk is filling up with data, you can try deleting files
from /var/log
, /var/crash
,
/var/lib/systemd/coredump
and
/var/cache
.
The Btrfs root
file system subvolumes /var/log
,
/var/crash
and /var/cache
can
use all of the available disk space during normal operation, and cause a
system malfunction. To help avoid this situation, SUSE Linux Enterprise Server offers
Btrfs quota support for subvolumes. See
Section 1.2.5, “Btrfs Quota Support for Subvolumes” for details.
On test and development machines, especially if you have frequent crashes
of applications, you may also want to have a look at
/var/lib/systemd/coredump
where the coredumps are
stored.
1.14.2 Btrfs: Balancing Data across Devices #
The btrfs balance
command is part of the
btrfs-progs package. It balances block groups on Btrfs
file systems in the following example situations:
Assume you have 1 TB drive with 600 GB used by data and you add another 1 TB drive. The balancing will theoretically result in having 300 GB used space on each drive.
You have a lot of near-empty chunks on a device. Their space will not be available until the balancing has cleared those chunks.
You need to compact half-empty block group based on the percentage of their usage. The following command will balance block groups whose usage is 5 % or less:
>
sudo
btrfs balance start -dusage=5 /TipThe
/usr/lib/systemd/system/btrfs-balance.timer
timer takes care of cleaning up unused block groups on a monthly basis.You need to clear out non-full portions of block devices and spread data more evenly.
You need to migrate data between different RAID types. For example, to convert data on a set of disks from RAID1 to RAID5, run the following command:
>
sudo
btrfs balance start -dprofiles=raid1,convert=raid5 /
To fine-tune the default behavior of balancing data on Btrfs file
systems—for example, how frequently or which mount points to
balance— inspect and customize
/etc/sysconfig/btrfsmaintenance
. The relevant options
start with BTRFS_BALANCE_
.
For details about the btrfs balance
command usage, see
its manual pages (man 8 btrfs-balance
).
1.14.3 No Defragmentation on SSDs #
Linux file systems contain mechanisms to avoid data fragmentation and usually it is not necessary to defragment. However, there are use cases, where data fragmentation cannot be avoided and where defragmenting the hard disk significantly improves the performance.
This only applies to conventional hard disks. On solid state disks (SSDs) which use flash memory to store data, the firmware provides an algorithm that determines to which chips the data is written. Data is usually spread all over the device. Therefore defragmenting an SSD does not have the desired effect and will reduce the lifespan of an SSD by writing unnecessary data.
For the reasons mentioned above, SUSE explicitly recommends not to defragment SSDs. Some vendors also warn about defragmenting solid state disks. This includes, but it is not limited to the following:
HPE 3PAR StoreServ All-Flash
HPE 3PAR StoreServ Converged Flash
1.15 Additional Information #
Each of the file system projects described above maintains its own home page on which to find mailing list information, further documentation, and FAQs:
The Btrfs Wiki on Kernel.org: https://btrfs.wiki.kernel.org/
E2fsprogs: Ext2/3/4 File System Utilities: http://e2fsprogs.sourceforge.net/
The OCFS2 Project: https://oss.oracle.com/projects/ocfs2/
An in-depth comparison of file systems (not only Linux file systems) is available from the Wikipedia project in Comparison of File Systems (http://en.wikipedia.org/wiki/Comparison_of_file_systems#Comparison).
2 Resizing File Systems #
Resizing file systems—not to be confused with resizing partitions or volumes—can be used to make space available on physical volumes or to use additional space available on a physical volume.
2.1 Use Cases #
It is strongly recommended to use the YaST Partitioner to resize partitions or logical volumes. When doing so, the file system will automatically be adjusted to the new size of the partition or volume. However, there are some cases where you need to resize the file system manually, because they are not supported by YaST:
After having resized a virtual disk of a VM Guest.
After having resized a volume from a network-attached storage.
After having manually resized partitions (for example by using
fdisk
orparted
) or logical volumes (for example by usinglvresize
).When wanting to shrink Btrfs file systems (as of SUSE Linux Enterprise Server 12, YaST only supports growing Btrfs file systems).
2.2 Guidelines for Resizing #
Resizing any file system involves some risks that can potentially result in losing data.
To avoid data loss, ensure that you back up your data before you begin any resizing task.
Consider the following guidelines when planning to resize a file system.
2.2.1 File Systems that Support Resizing #
The file system must support resizing to take advantage of increases in available space for the volume. In SUSE Linux Enterprise Server, file system resizing utilities are available for file systems Ext2, Ext3, and Ext4. The utilities support increasing and decreasing the size as follows:
File System |
Utility |
Increase Size (Grow) |
Decrease Size (Shrink) |
---|---|---|---|
Btrfs |
|
Online |
Online |
XFS |
|
Online |
Not supported |
Ext2 |
|
Online or offline |
Offline only |
Ext3 |
|
Online or offline |
Offline only |
Ext4 |
|
Online or offline |
Offline only |
2.2.2 Increasing the Size of a File System #
You can grow a file system to the maximum space available on the device, or specify an exact size. Ensure that you grow the size of the device or logical volume before you attempt to increase the size of the file system.
When specifying an exact size for the file system, ensure that the new size satisfies the following conditions:
The new size must be greater than the size of the existing data; otherwise, data loss occurs.
The new size must be equal to or less than the current device size because the file system size cannot extend beyond the space available.
2.2.3 Decreasing the Size of a File System #
When decreasing the size of the file system on a device, ensure that the new size satisfies the following conditions:
The new size must be greater than the size of the existing data; otherwise, data loss occurs.
The new size must be equal to or less than the current device size because the file system size cannot extend beyond the space available.
If you plan to also decrease the size of the logical volume that holds the file system, ensure that you decrease the size of the file system before you attempt to decrease the size of the device or logical volume.
Decreasing the size of a file system formatted with XFS is not possible, since such a feature is not supported by XFS.
2.3 Changing the Size of a Btrfs File System #
The size of a Btrfs file system can be changed by using the btrfs
filesystem resize
command when the file system is mounted.
Increasing and decreasing the size are both supported while the file system
is mounted.
Open a terminal.
Make sure the file system you want to change is mounted.
Change the size of the file system using the
btrfs filesystem resize
command with one of the following methods:To extend the file system size to the maximum available size of the device, enter
>
sudo
btrfs filesystem resize max /mntTo extend the file system to a specific size, enter
>
sudo
btrfs filesystem resize SIZE /mntReplace SIZE with the desired size in bytes. You can also specify units on the value, such as 50000K (kilobytes), 250M (megabytes), or 2G (gigabytes). Alternatively, you can specify an increase or decrease to the current size by prefixing the value with a plus (
+
) or a minus (-
) sign, respectively:>
sudo
btrfs filesystem resize +SIZE /mnt sudo btrfs filesystem resize -SIZE /mnt
Check the effect of the resize on the mounted file system by entering
>
df -hThe Disk Free (
df
) command shows the total size of the disk, the number of blocks used, and the number of blocks available on the file system. The -h option prints sizes in human-readable format, such as 1K, 234M, or 2G.
2.4 Changing the Size of an XFS File System #
The size of an XFS file system can be increased by using the
xfs_growfs
command when the file system is mounted.
Reducing the size of an XFS file system is not possible.
Open a terminal.
Make sure the file system you want to change is mounted.
Increase the size of the file system using the
xfs_growfs
command. The following example expands the size of the file system to the maximum value available. Seeman 8 xfs_growfs
for more options.>
sudo
xfs_growfs -d /mntCheck the effect of the resize on the mounted file system by entering
>
df -hThe Disk Free (
df
) command shows the total size of the disk, the number of blocks used, and the number of blocks available on the file system. The -h option prints sizes in human-readable format, such as 1K, 234M, or 2G.
2.5 Changing the Size of an Ext2, Ext3, or Ext4 File System #
The size of Ext2, Ext3, and Ext4 file systems can be increased by using the
resize2fs
command, regardless of whether the respective
partition is mounted or not. To decrease the size of an Ext file system it
needs to be unmounted.
Open a terminal.
If the file system size should be decreased, unmount it.
Change the size of the file system using one of the following methods:
To extend the file system size to the maximum available size of the device called
/dev/sda1
, enter>
sudo
resize2fs /dev/sda1If a size parameter is not specified, the size defaults to the size of the partition.
To change the file system to a specific size, enter
>
sudo
resize2fs /dev/sda1 SIZEThe SIZE parameter specifies the requested new size of the file system. If no units are specified, the unit of the size parameter is the block size of the file system. Optionally, the size parameter can be suffixed by one of the following unit designations:
s
for 512 byte sectors;K
for kilobytes (1 kilobyte is 1024 bytes);M
for megabytes; orG
for gigabytes.
Wait until the resizing is completed before continuing.
If the file system is not mounted, mount it now.
Check the effect of the resize on the mounted file system by entering
>
df -hThe Disk Free (
df
) command shows the total size of the disk, the number of blocks used, and the number of blocks available on the file system. The -h option prints sizes in human-readable format, such as 1K, 234M, or 2G.
3 Mounting storage devices #
This section gives an overview which device identificators are used during mounting of devices, and provides details about mounting network storages.
3.1 Understanding UUIDs #
A UUID (Universally Unique Identifier) is a 128-bit number for a file system that is unique on both the local system and across other systems. It is randomly generated with system hardware information and time stamps as part of its seed. UUIDs are commonly used to uniquely tag devices.
Using non-persistent “traditional” device names such as
/dev/sda1
may render the system unbootable when adding
storage. For example, if root (/
) is assigned to
/dev/sda1
, it might be reassigned to
/dev/sdg1
after a SAN has been attached or additional
hard disks have been applied to the system. In this case the boot loader
configuration and the /etc/fstab
file need to be
adjusted, otherwise the system will no longer boot.
By default UUID are used in the boot loader and
/etc/fstab
files for the boot device. The UUID is a
property of the file system and can change if you reformat the drive. Other
alternatives to using UUIDs of device names would be to identify devices by
ID or label.
You can also use the UUID as criterion for assembling and activating
software RAID devices. When a RAID is created, the md
driver generates a UUID for the device, and stores the value in the
md
superblock.
You can find the UUID for any block device in the
/dev/disk/by-uuid
directory. For example, a UUID entry
looks like this:
>
ls -og /dev/disk/by-uuid/
lrwxrwxrwx 1 10 Dec 5 07:48 e014e482-1c2d-4d09-84ec-61b3aefde77a -> ../../sda1
3.2 Persistent device names with udev #
Starting with Linux kernel 2.6, udev
provides a user
space solution for the dynamic /dev
directory, with
persistent device naming. As part of the hotplug system,
udev
is executed if a device is added to or removed from
the system.
A list of rules is used to match against specific device attributes. The
udev
rules infrastructure (defined in the
/etc/udev/rules.d
directory) provides stable names for
all disk devices, regardless of their order of recognition or the connection
used for the device. The udev
tools examine every
appropriate block device that the kernel creates to apply naming rules based
on certain buses, drive types, or file systems. For information about how to
define your own rules for udev
, see
Writing
udev Rules.
Along with the dynamic kernel-provided device node name,
udev
maintains classes of persistent symbolic links
pointing to the device in the /dev/disk
directory,
which is further categorized by the by-id
,
by-label
, by-path
, and
by-uuid
subdirectories.
Other programs besides udev
, such as LVM or
md
, might also generate UUIDs, but they are not listed
in /dev/disk
.
For more information about using udev
for managing
devices, see Book “Administration Guide”, Chapter 24 “Dynamic Kernel Device Management with udev
”.
For more information about udev
commands, see
man 7 udev
.
3.3 Mounting network storage devices #
Some types of storage devices require network to be configured and available
before systemd.mount
starts to mount the devices. To
postpone mounting of these types of devices, add the
_netdev
and x-systemd.requires=iscsi.service
options to the /etc/fstab
file for each particular network storage device. An example follows:
mars.example.org:/nfsexport /shared nfs defaults,_netdev,x-systemd.requires=iscsi.service 0 0
Do not use the nofail
option as booting of the machine continues without waiting
for the particular storage device to be successfully mounted.
4 Multi-tier Caching for Block Device Operations #
A multi-tier cache is a replicated/distributed cache that consists of at least two tiers: one is represented by slower but cheaper rotational block devices (hard disks), while the other is more expensive but performs faster data operations (for example SSD flash disks).
SUSE Linux Enterprise Server implements two different solutions for caching between flash and
rotational devices: bcache
and lvmcache
.
4.1 General Terminology #
This section explains several terms often used when describing cache related features:
- Migration
Movement of the primary copy of a logical block from one device to the other.
- Promotion
Migration from the slow device to the fast device.
- Demotion
Migration from the fast device to the slow device.
- Origin device
The big and slower block device. It always contains a copy of the logical block, which may be out of date or kept in synchronization with the copy on the cache device (depending on policy).
- Cache device
The small and faster block device.
- Metadata device
A small device that records which blocks are in the cache, which are dirty, and extra hints for use by the policy object. This information could be put on the cache device as well, but having it separate allows the volume manager to configure it differently, for example as a mirror for extra robustness. The metadata device may only be used by a single cache device.
- Dirty block
If some process writes to a block of data which is placed in the cache, the cached block is marked as dirty because it was overwritten in the cache and needs to be written back to the original device.
- Cache miss
A request for I/O operations is pointed to the cached device's cache first. If it cannot find the requested values, it looks in the device itself, which is slow. This is called a cache miss.
- Cache hit
When a requested value is found in the cached device's cache, it is served fast. This is called a cache hit.
- Cold cache
Cache that holds no values (is empty) and causes cache misses. As the cached block device operations progress, it gets filled with data and becomes warm.
- Warm cache
Cache that already holds some values and is likely to result in cache hits.
4.2 Caching Modes #
Following are the basic caching modes that multi-tier caches use: write-back, write-through, write-around and pass-through.
- write-back
Data written to a block that is cached go to the cache only, and the block is marked dirty. This is the default caching mode.
- write-through
Writing to a cached block will not complete until it has hit both the origin and cache devices. Clean blocks remain clean with write-through cache.
- write-around
A similar technique to write-through cache, but write I/O is written directly to a permanent storage, bypassing the cache. This can prevent the cache being flooded with write I/O that will not subsequently be re-read, but the disadvantage is that a read request for recently written data will create a 'cache miss' and needs to be read from slower bulk storage and experience higher latency.
- pass-through
To enable the pass-through mode, the cache needs to be clean. Reading is served from the origin device bypassing the cache. Writing is forwarded to the origin device and 'invalidates' the cache block. Pass-through allows a cache device activation without having to care about data coherency, which is maintained. The cache will gradually become cold as writing takes place. If you can verify the coherency of the cache later, or establish it by using the
invalidate_cblocks
message, you can switch the cache device to write-through or write-back mode while it is still warm. Otherwise, you can discard the cache contents before switching to the desired caching mode.
4.3 bcache
#
bcache
is a Linux kernel block layer cache. It allows one or more fast
disk drives (such as SSDs) to act as a cache for one or more slower hard
disks. bcache
supports write-through and write-back, and is independent of
the file system used. By default it caches random reads and writes only,
which SSDs excel at. It is suitable for desktops, servers, and high end
storage arrays as well.
4.3.1 Main Features #
A single cache device can be used to cache an arbitrary number of backing devices. Backing devices can be attached and detached at runtime, while mounted and in use.
Recovers from unclean shutdowns—writes are not completed until the cache is consistent with regard to the backing device.
Throttles traffic to the SSD if it becomes congested.
Highly efficient write-back implementation. Dirty data is always written out in sorted order.
Stable and reliable—in production use.
4.3.2 Setting Up a bcache
Device #
This section describes steps to set up and manage a bcache
device.
Install the
bcache-tools
package:>
sudo
zypper in bcache-toolsCreate a backing device (typically a mechanical drive). The backing device can be a whole device, a partition, or any other standard block device.
>
sudo
make-bcache -B /dev/sdbCreate a cache device (typically an SSD disk).
>
sudo
make-bcache -C /dev/sdcIn this example, the default block and bucket sizes of 512 B and 128 KB are used. The block size should match the backing device's sector size which will usually be either 512 or 4k. The bucket size should match the erase block size of the caching device with the intention of reducing write amplification. For example, using a hard disk with 4k sectors and an SSD with an erase block size of 2 MB this command would look as follows:
sudo make-bcache --block 4k --bucket 2M -C /dev/sdc
Tip: Multi-Device Supportmake-bcache
can prepare and register multiple backing devices and a cache device at the same time. In this case you do not need to manually attach the cache device to the backing device afterward:>
sudo
make-bcache -B /dev/sda /dev/sdb -C /dev/sdcbcache
devices show up as/dev/bcacheN
and as
/dev/bcache/by-uuid/UUID /dev/bcache/by-label/LABEL
You can normally format and mount
bcache
devices as usual:>
sudo
mkfs.ext4 /dev/bcache0>
sudo
mount /dev/bcache0 /mntYou can control
bcache
devices throughsysfs
at/sys/block/bcacheN/bcache
.After both the cache and backing devices are registered, you need to attach the backing device to the related cache set to enable caching:
>
echo CACHE_SET_UUID > /sys/block/bcache0/bcache/attachwhere CACHE_SET_UUID is found in
/sys/fs/bcache
.By default
bcache
uses a pass-through caching mode. To change it to for example write-back, run>
echo writeback > /sys/block/bcache0/bcache/cache_mode
4.3.3 bcache
Configuration Using sysfs
#
bcache
devices use the sysfs
interface to store
their runtime configuration values. This way you can change bcache
backing and cache disks' behavior or see their usage statistics.
For the complete list of bcache
sysfs
parameters, see the contents of the
/usr/src/linux/Documentation/bcache.txt
file, mainly
the SYSFS - BACKING DEVICE
, SYSFS - BACKING
DEVICE STATS
, and SYSFS - CACHE DEVICE
sections.
4.4 lvmcache
#
lvmcache
is a caching mechanism consisting of logical volumes (LVs). It
uses the dm-cache
kernel driver and supports
write-through (default) and write-back caching modes. lvmcache
improves
performance of a large and slow LV by dynamically migrating some of its data
to a faster and smaller LV. For more information on LVM, see
Part II, “Logical Volumes (LVM)”.
LVM refers to the small, fast LV as a cache pool LV. The large, slow LV is called the origin LV. Because of requirements from dm-cache, LVM further splits the cache pool LV into two devices: the cache data LV and cache metadata LV. The cache data LV is where copies of data blocks are kept from the origin LV to increase speed. The cache metadata LV holds the accounting information that specifies where data blocks are stored.
4.4.1 Configuring lvmcache
#
This section describes steps to create and configure LVM based caching.
Create the origin LV. Create a new LV or use an existing LV to become the origin LV:
>
sudo
lvcreate -n ORIGIN_LV -L 100G vg /dev/SLOW_DEVCreate the cache data LV. This LV will hold data blocks from the origin LV. The size of this LV is the size of the cache and will be reported as the size of the cache pool LV.
>
sudo
lvcreate -n CACHE_DATA_LV -L 10G vg /dev/FASTCreate the cache metadata LV. This LV will hold cache pool metadata. The size of this LV should be approximately 1000 times smaller than the cache data LV, with a minimum size of 8MB.
>
sudo
lvcreate -n CACHE_METADATA_LV -L 12M vg /dev/FASTList the volumes you have created so far:
>
sudo
lvs -a vg LV VG Attr LSize Pool Origin cache_data_lv vg -wi-a----- 10.00g cache_metadata_lv vg -wi-a----- 12.00m origin_lv vg -wi-a----- 100.00gCreate a cache pool LV. Combine the data and metadata LVs into a cache pool LV. You can set the cache pool LV's behavior at the same time.
CACHE_POOL_LV takes the name of CACHE_DATA_LV.
CACHE_DATA_LV is renamed to CACHE_DATA_LV_cdata and becomes hidden.
CACHE_META_LV is renamed to CACHE_DATA_LV_cmeta and becomes hidden.
>
sudo
lvconvert --type cache-pool \ --poolmetadata vg/cache_metadata_lv vg/cache_data_lv>
sudo
lvs -a vg LV VG Attr LSize Pool Origin cache_data_lv vg Cwi---C--- 10.00g [cache_data_lv_cdata] vg Cwi------- 10.00g [cache_data_lv_cmeta] vg ewi------- 12.00m origin_lv vg -wi-a----- 100.00gCreate a cache LV. Create a cache LV by linking the cache pool LV to the origin LV.
The user accessible cache LV takes the name of the origin LV, while the origin LV becomes a hidden LV renamed to ORIGIN_LV_corig.
CacheLV takes the name of ORIGIN_LV.
ORIGIN_LV is renamed to ORIGIN_LV_corig and becomes hidden.
>
sudo
lvconvert --type cache --cachepool vg/cache_data_lv vg/origin_lv>
sudo
lvs -a vg LV VG Attr LSize Pool Origin cache_data_lv vg Cwi---C--- 10.00g [cache_data_lv_cdata] vg Cwi-ao---- 10.00g [cache_data_lv_cmeta] vg ewi-ao---- 12.00m origin_lv vg Cwi-a-C--- 100.00g cache_data_lv [origin_lv_corig] [origin_lv_corig] vg -wi-ao---- 100.00g
4.4.2 Removing a Cache Pool #
There are several ways to turn off the LV cache.
4.4.2.1 Detach a Cache Pool LV from a Cache LV #
You can disconnect a cache pool LV from a cache LV, leaving an unused cache pool LV and an uncached origin LV. Data are written back from the cache pool to the origin LV when necessary.
>
sudo
lvconvert --splitcache vg/origin_lv
4.4.2.2 Removing a Cache Pool LV without Removing its Origin LV #
This writes back data from the cache pool to the origin LV when necessary, then removes the cache pool LV, leaving the uncached origin LV.
>
sudo
lvremove vg/cache_data_lv
An alternative command that also disconnects the cache pool from the cache LV, and deletes the cache pool:
>
sudo
lvconvert --uncache vg/origin_lv
4.4.2.3 Removing Both the Origin LV and the Cache Pool LV #
Removing a cache LV removes both the origin LV and the linked cache pool LV.
>
sudo
lvremove vg/origin_lv
4.4.2.4 For More Information #
You can find more lvmcache
related topics, such as supported cache
modes, redundant sub-logical volumes, cache policy, or converting existing
LVs to cache types, in the lvmcache
manual page (man 7
lvmcache
).
Part II Logical Volumes (LVM) #
- 5 LVM Configuration
This chapter describes the principles behind Logical Volume Manager (LVM) and its basic features that make it useful under many circumstances. The YaST LVM configuration can be reached from the YaST Expert Partitioner. This partitioning tool enables you to edit and delete existing partitions and create new ones that should be used with LVM.
- 6 LVM Volume Snapshots
A Logical Volume Manager (LVM) logical volume snapshot is a copy-on-write technology that monitors changes to an existing volume’s data blocks so that when a write is made to one of the blocks, the block’s value at the snapshot time is copied to a snapshot volume. In this way, a point-in-time copy o…
5 LVM Configuration #
This chapter describes the principles behind Logical Volume Manager (LVM) and its basic features that make it useful under many circumstances. The YaST LVM configuration can be reached from the YaST Expert Partitioner. This partitioning tool enables you to edit and delete existing partitions and create new ones that should be used with LVM.
Using LVM might be associated with increased risk, such as data loss. Risks also include application crashes, power failures, and faulty commands. Save your data before implementing LVM or reconfiguring volumes. Never work without a backup.
5.1 Understanding the Logical Volume Manager #
LVM enables flexible distribution of hard disk space over several physical volumes (hard disks, partitions, LUNs). It was developed because the need to change the segmentation of hard disk space might arise only after the initial partitioning has already been done during installation. Because it is difficult to modify partitions on a running system, LVM provides a virtual pool (volume group or VG) of storage space from which logical volumes (LVs) can be created as needed. The operating system accesses these LVs instead of the physical partitions. Volume groups can span more than one disk, so that several disks or parts of them can constitute one single VG. In this way, LVM provides a kind of abstraction from the physical disk space that allows its segmentation to be changed in a much easier and safer way than through physical repartitioning.
Figure 5.1, “Physical Partitioning versus LVM” compares physical partitioning (left) with LVM segmentation (right). On the left side, one single disk has been divided into three physical partitions (PART), each with a mount point (MP) assigned so that the operating system can access them. On the right side, two disks have been divided into two and three physical partitions each. Two LVM volume groups (VG 1 and VG 2) have been defined. VG 1 contains two partitions from DISK 1 and one from DISK 2. VG 2 contains the remaining two partitions from DISK 2.
In LVM, the physical disk partitions that are incorporated in a volume group are called physical volumes (PVs). Within the volume groups in Figure 5.1, “Physical Partitioning versus LVM”, four logical volumes (LV 1 through LV 4) have been defined, which can be used by the operating system via the associated mount points (MP). The border between different logical volumes need not be aligned with any partition border. See the border between LV 1 and LV 2 in this example.
LVM features:
Several hard disks or partitions can be combined in a large logical volume.
Provided the configuration is suitable, an LV (such as
/usr
) can be enlarged when the free space is exhausted.Using LVM, it is possible to add hard disks or LVs in a running system. However, this requires hotpluggable hardware that is capable of such actions.
It is possible to activate a striping mode that distributes the data stream of a logical volume over several physical volumes. If these physical volumes reside on different disks, this can improve the reading and writing performance like RAID 0.
The snapshot feature enables consistent backups (especially for servers) in the running system.
Even though LVM also supports RAID of 0/1/4/5/6 levels, we recommend to use MD RAID (see Chapter 7, Software RAID Configuration). However, LVM works fine with RAID 0 and 1, as RAID 0 is similar to common logical volume management (individual logical blocks are mapped onto blocks on the physical devices). LVM used on top of RAID 1 can keep track of mirror synchronization and is fully able to manage the synchronization process. With higher RAID levels you need a management daemon that monitors the states of attached disks and can inform administrators if there is a problem in the disk array. LVM includes such a daemon, but in exceptional situations like a device failure, the daemon does not working properly.
If you configure the system with a root file system on LVM or software
RAID array, you must place /boot
on a separate,
non-LVM or non-RAID partition, otherwise the system will fail to boot.
The recommended size for such a partition is 500 MB and the
recommended file system is Ext4.
With these features, using LVM already makes sense for heavily used home PCs or small servers. If you have a growing data stock, as in the case of databases, music archives, or user directories, LVM is especially useful. It allows file systems that are larger than the physical hard disk. However, keep in mind that working with LVM is different from working with conventional partitions.
You can manage new or existing LVM storage objects by using the YaST Partitioner. Instructions and further information about configuring LVM are available in the official LVM HOWTO.
5.2 Creating Volume Groups #
An LVM volume group (VG) organizes the Linux LVM partitions into a logical pool of space. You can carve out logical volumes from the available space in the group. The Linux LVM partitions in a group can be on the same or different disks. You can add partitions or entire disks to expand the size of the group.
To use an entire disk, it must not contain any
partitions. When using partitions, they must not be mounted. YaST will
automatically change their partition type to 0x8E Linux
LVM
when adding them to a VG.
Launch YaST and open the
.In case you need to reconfigure your existing partitioning setup, proceed as follows. Refer to Book “Deployment Guide”, Chapter 10 “Expert Partitioner”, Section 10.1 “Using the Expert Partitioner” for details. Skip this step if you only want to use unused disks or partitions that already exist.
Warning: Physical Volumes on Unpartitioned DisksYou can use an unpartitioned disk as a physical volume (PV) if that disk is not the one where the operating system is installed and from which it boots.
As unpartitioned disks appear as unused at the system level, they can easily be overwritten or wrongly accessed.
To use an entire hard disk that already contains partitions, delete all partitions on that disk.
To use a partition that is currently mounted, unmount it.
In the left panel, select
.A list of existing Volume Groups opens in the right panel.
At the lower left of the Volume Management page, click
.Define the volume group as follows:
Specify the
.If you are creating a volume group at install time, the name
system
is suggested for a volume group that will contain the SUSE Linux Enterprise Server system files.Specify the
.The
defines the size of a physical block in the volume group. All the disk space in a volume group is handled in chunks of this size. Values can be from 1 KB to 16 GB in powers of 2. This value is normally set to 4 MB.In LVM1, a 4 MB physical extent allowed a maximum LV size of 256 GB because it supports only up to 65534 extents per LV. LVM2, which is used on SUSE Linux Enterprise Server, does not restrict the number of physical extents. Having many extents has no impact on I/O performance to the logical volume, but it slows down the LVM tools.
Important: Physical Extent SizesDifferent physical extent sizes should not be mixed in a single VG. The extent should not be modified after the initial setup.
In the
list, select the Linux LVM partitions that you want to make part of this volume group, then click to move them to the list.Click
.The new group appears in the
list.
On the Volume Management page, click
, verify that the new volume group is listed, then click .To check which physical devices are part of the volume group, open the YaST Partitioner at any time in the running system and click
› › . Leave this screen with .Figure 5.2: Physical Volumes in the Volume Group Named DATA #
5.3 Creating Logical Volumes #
A logical volume provides a pool of space similar to what a hard disk does. To make this space usable, you need to define logical volumes. A logical volume is similar to a regular partition—you can format and mount it.
Use The YaST Partitioner to create logical volumes from an existing volume group. Assign at least one logical volume to each volume group. You can create new logical volumes as needed until all free space in the volume group has been exhausted. An LVM logical volume can optionally be thinly provisioned, allowing you to create logical volumes with sizes that overbook the available free space (see Section 5.3.1, “Thinly Provisioned Logical Volumes” for more information).
Normal volume: (Default) The volume’s space is allocated immediately.
Thin pool: The logical volume is a pool of space that is reserved for use with thin volumes. The thin volumes can allocate their needed space from it on demand.
Thin volume: The volume is created as a sparse volume. The volume allocates needed space on demand from a thin pool.
Mirrored volume: The volume is created with a defined count of mirrors.
Launch YaST and open the
.In the left panel, select
. A list of existing Volume Groups opens in the right panel.Select the volume group in which you want to create the volume and choose
› .Provide a Section 5.3.1, “Thinly Provisioned Logical Volumes” for setting up thinly provisioned volumes). Proceed with .
for the volume and choose (refer toSpecify the size of the volume and whether to use multiple stripes.
Using a striped volume, the data will be distributed among several physical volumes. If these physical volumes reside on different hard disks, this generally results in a better reading and writing performance (like RAID 0). The maximum number of available stripes is equal to the number of physical volumes. The default (
1
is to not use multiple stripes.Choose a
for the volume. Your choice here only affects the default values for the upcoming dialog. They can be changed in the next step. If in doubt, choose .Under
, select , then select the . The content of the menu depends on the file system. Usually there is no need to change the defaults.Under
, select , then select the mount point. Click to add special mounting options for the volume.Click
.Click
, verify that the changes are listed, then click .
5.3.1 Thinly Provisioned Logical Volumes #
An LVM logical volume can optionally be thinly provisioned. Thin provisioning allows you to create logical volumes with sizes that overbook the available free space. You create a thin pool that contains unused space reserved for use with an arbitrary number of thin volumes. A thin volume is created as a sparse volume and space is allocated from a thin pool as needed. The thin pool can be expanded dynamically when needed for cost-effective allocation of storage space. Thinly provisioned volumes also support snapshots which can be managed with Snapper—see Book “Administration Guide”, Chapter 7 “System Recovery and Snapshot Management with Snapper” for more information.
To set up a thinly provisioned logical volume, proceed as described in Procedure 5.1, “Setting Up a Logical Volume”. When it comes to choosing the volume type, do not choose , but rather or .
The logical volume is a pool of space that is reserved for use with thin volumes. The thin volumes can allocate their needed space from it on demand.
The volume is created as a sparse volume. The volume allocates needed space on demand from a thin pool.
To use thinly provisioned volumes in a cluster, the thin pool and the thin volumes that use it must be managed in a single cluster resource. This allows the thin volumes and thin pool to always be mounted exclusively on the same node.
5.3.2 Creating Mirrored Volumes #
A logical volume can be created with several mirrors. LVM ensures that data written to an underlying physical volume is mirrored onto a different physical volume. Thus even though a physical volume crashes, you can still access the data on the logical volume. LVM also keeps a log file to manage the synchronization process. The log contains information about which volume regions are currently undergoing synchronization with mirrors. By default the log is stored on disk and if possible on a different disk than are the mirrors. But you may specify a different location for the log, for example volatile memory.
Currently there are two types of mirror implementation available:
"normal" (non-raid) mirror
logical volumes and
raid1
logical volumes.
After you create mirrored logical volumes, you can perform standard operations with mirrored logical volumes like activating, extending, and removing.
5.3.2.1 Setting Up Mirrored Non-raid Logical Volumes #
To create a mirrored volume use the lvcreate
command.
The following example creates a 500 GB logical volume with two mirrors
called lv1 which uses a volume group
vg1.
>
sudo
lvcreate -L 500G -m 2 -n lv1 vg1
Such a logical volume is a linear volume (without striping) that provides
three copies of the file system. The m
option specifies
the count of mirrors. The L
option specifies the size
of the logical volumes.
The logical volume is divided into regions of the 512 KB default size. If
you need a different size of regions, use the -R
option
followed by the desired region size in megabytes. Or you can configure the
preferred region size by editing the mirror_region_size
option in the lvm.conf
file.
5.3.2.2 Setting Up raid1
Logical Volumes #
As LVM supports RAID you can implement mirroring by using RAID1. Such implementation provides the following advantages compared to the non-raid mirrors:
LVM maintains a fully redundant bitmap area for each mirror image, which increases its fault handling capabilities.
Mirror images can be temporarily split from the array and then merged back.
The array can handle transient failures.
The LVM RAID 1 implementation supports snapshots.
On the other hand, this type of mirroring implementation does not enable to create a logical volume in a clustered volume group.
To create a mirror volume by using RAID, issue the command
>
sudo
lvcreate --type raid1 -m 1 -L 1G -n lv1 vg1
where the options/parameters have the following meanings:
--type
- you need to specifyraid1
, otherwise the command uses the implicit segment typemirror
and creates a non-raid mirror.-m
- specifies the count of mirrors.-L
- specifies the size of the logical volume.-n
- by using this option you specify a name of the logical volume.vg1
- is a name of the volume group used by the logical volume.
LVM creates a logical volume of one extent size for each data volume in the array. If you have two mirrored volumes, LVM creates another two volumes that stores metadata.
After you create a RAID logical volume, you can use the volume in the same way as a common logical volume. You can activate it, extend it, etc.
5.4 Automatically Activating Non-Root LVM Volume Groups #
Activation behavior for non-root LVM volume groups is controlled in the
/etc/lvm/lvm.conf
file and by the
auto_activation_volume_list parameter. By default,
the parameter is empty and all volumes are activated. To activate only some
volume groups, add the names in quotes and separate them with commas, for
example:
auto_activation_volume_list = [ "vg1", "vg2/lvol1", "@tag1", "@*" ]
If you have defined a list in the auto_activation_volume_list parameter, the following will happen:
Each logical volume is first checked against this list.
If it does not match, the logical volume will not be activated.
By default, non-root LVM volume groups are automatically activated on system restart by Dracut. This parameter allows you to activate all volume groups on system restart, or to activate only specified non-root LVM volume groups.
5.5 Resizing an Existing Volume Group #
The space provided by a volume group can be expanded at any time in the running system without service interruption by adding physical volumes. This will allow you to add logical volumes to the group or to expand the size of existing volumes as described in Section 5.6, “Resizing a Logical Volume”.
It is also possible to reduce the size of the volume group by removing
physical volumes. YaST only allows to remove physical volumes that are
currently unused. To find out which physical volumes are currently in use,
run the following command. The partitions (physical volumes) listed in the
PE Ranges
column are the ones in use:
>
sudo
pvs -o vg_name,lv_name,pv_name,seg_pe_ranges root's password: VG LV PV PE Ranges /dev/sda1 DATA DEVEL /dev/sda5 /dev/sda5:0-3839 DATA /dev/sda5 DATA LOCAL /dev/sda6 /dev/sda6:0-2559 DATA /dev/sda7 DATA /dev/sdb1 DATA /dev/sdc1
Launch YaST and open the
.In the left panel, select
. A list of existing Volume Groups opens in the right panel.Select the volume group you want to change, activate the
tab, then click .Do one of the following:
Add: Expand the size of the volume group by moving one or more physical volumes (LVM partitions) from the list to the list.
Remove: Reduce the size of the volume group by moving one or more physical volumes (LVM partitions) from the list to the list.
Click
.Click
, verify that the changes are listed, then click .
5.6 Resizing a Logical Volume #
In case there is unused free space available in the volume group, you can enlarge a logical volume to provide more usable space. You may also reduce the size of a volume to free space in the volume group that can be used by other logical volumes.
When reducing the size of a volume, YaST automatically resizes its file system, too. Whether a volume that is currently mounted can be resized “online” (that is while being mounted), depends on its file system. Growing the file system online is supported by Btrfs, XFS, Ext3, and Ext4.
Shrinking the file system online is only supported by Btrfs. To shrink the Ext2/3/4 file systems, you need to unmount them. Shrinking volumes formatted with XFS is not possible, since XFS does not support file system shrinking.
Launch YaST and open the
.In the left panel, select
. A list of existing Volume Groups opens in the right panel.Select the logical volume you want to change, then click
.Set the intended size by using one of the following options:
Maximum Size. Expand the size of the logical volume to use all space left in the volume group.
Minimum Size. Reduce the size of the logical volume to the size occupied by the data and the file system metadata.
Custom Size. Specify the new size for the volume. The value must be within the range of the minimum and maximum values listed above. Use K, M, G, T for Kilobytes, Megabytes, Gigabytes and Terabytes (for example
20G
).
Click
.Click
, verify that the change is listed, then click .
5.7 Deleting a Volume Group or a Logical Volume #
Deleting a volume group destroys all of the data in each of its member partitions. Deleting a logical volume destroys all data stored on the volume.
Launch YaST and open the
.In the left panel, select
. A list of existing volume groups opens in the right panel.Select the volume group or the logical volume you want to remove and click
.Depending on your choice warning dialogs are shown. Confirm them with
.Click
, verify that the deleted volume group is listed (deletion is indicated by a red colored font), then click .
5.8 Disabling LVM on boot #
If there is an error on the LVM storage, the scanning of LVM volumes may
prevent entering the emergency/rescue shell. Thus, further problem diagnosis
is not possible. To disable this scanning in case of an LVM storage failure,
you can pass the nolvm
option on the kernel command line.
5.9 Using LVM Commands #
For information about using LVM commands, see the man pages for the commands
described in the following table. All commands need to be executed with
root
privileges. Either use sudo
COMMAND (recommended) or execute them directly as
root
.
pvcreate DEVICE
Initializes a device (such as
/dev/sdb1
) for use by LVM as a physical volume. If there is any file system on the specified device, a warning appears. Bear in mind thatpvcreate
checks for existing file systems only ifblkid
is installed (which is done by default). Ifblkid
is not available,pvcreate
will not produce any warning and you may lose your file system without any warning.pvdisplay DEVICE
Displays information about the LVM physical volume, such as whether it is currently being used in a logical volume.
-
vgcreate -c y VG_NAME DEV1 [DEV2...]
Creates a clustered volume group with one or more specified devices.
-
vgcreate --activationmode ACTIVATION_MODE VG_NAME
Configures the mode of volume group activation. You can specify one of the following values:
complete
- only the logical volumes that are not affected by missing physical volumes can be activated, even though the particular logical volume can tolerate such a failure.degraded
- is the default activation mode. If there is a sufficient level of redundancy to activate a logical volume, the logical volume can be activated even though some physical volumes are missing.partial
- the LVM tries to activate the volume group even though some physical volumes are missing. If a non-redundant logical volume is missing important physical volumes, then the logical volume usually cannot be activated and is handled as an error target.
-
vgchange -a [ey|n] VG_NAME
Activates (
-a ey
) or deactivates (-a n
) a volume group and its logical volumes for input/output.When activating a volume in a cluster, ensure that you use the
ey
option. This option is used by default in the load script.vgremove VG_NAME
Removes a volume group. Before using this command, remove the logical volumes, then deactivate the volume group.
-
vgdisplay VG_NAME
Displays information about a specified volume group.
To find the total physical extent of a volume group, enter
>
vgdisplay VG_NAME | grep "Total PE"-
lvcreate -L SIZE -n LV_NAME VG_NAME
Creates a logical volume of the specified size.
-
lvcreate -L SIZE --thinpool POOL_NAME VG_NAME
Creates a thin pool named
myPool
of the specified size from the volume group VG_NAME.The following example creates a thin pool with a size of 5 GB from the volume group
LOCAL
:>
sudo
lvcreate -L 5G --thinpool myPool LOCAL-
lvcreate -T VG_NAME/POOL_NAME -V SIZE -n LV_NAME
Creates a thin logical volume within the pool POOL_NAME. The following example creates a 1GB thin volume named
myThin1
from the poolmyPool
on the volume groupLOCAL
:>
sudo
lvcreate -T LOCAL/myPool -V 1G -n myThin1-
lvcreate -T VG_NAME/POOL_NAME -V SIZE -L SIZE -n LV_NAME
It is also possible to combine thin pool and thin logical volume creation in one command:
>
sudo
lvcreate -T LOCAL/myPool -V 1G -L 5G -n myThin1-
lvcreate --activationmode ACTIVATION_MODE LV_NAME
Configures the mode of logical volume activation. You can specify one of the following values:
complete
- the logical volume can be activated only if all its physical volumes are active.degraded
- is the default activation mode. If there is a sufficient level of redundancy to activate a logical volume, the logical volume can be activated even though some physical volumes are missing.partial
- the LVM tries to activate the volume even though some physical volumes are missing. In this case part of the logical volume may be unavailable and it might cause data loss. This option is typically not used, but might be useful when restoring data.
You can specify the activation mode also in
/etc/lvm/lvm.conf
by specifying one of the above described values of theactivation_mode
configuration option.-
lvcreate -s [-L SIZE] -n SNAP_VOLUME SOURCE_VOLUME_PATH VG_NAME
Creates a snapshot volume for the specified logical volume. If the size option (
-L
or--size
) is not included, the snapshot is created as a thin snapshot.-
lvremove /dev/VG_NAME/LV_NAME
Removes a logical volume.
Before using this command, close the logical volume by unmounting it with the
umount
command.-
lvremove SNAP_VOLUME_PATH
Removes a snapshot volume.
-
lvconvert --merge SNAP_VOLUME_PATH
Reverts the logical volume to the version of the snapshot.
-
vgextend VG_NAME DEVICE
Adds the specified device (physical volume) to an existing volume group.
-
vgreduce VG_NAME DEVICE
Removes a specified physical volume from an existing volume group.
Ensure that the physical volume is not currently being used by a logical volume. If it is, you must move the data to another physical volume by using the
pvmove
command.-
lvextend -L SIZE /dev/VG_NAME/LV_NAME
Extends the size of a specified logical volume. Afterward, you must also expand the file system to take advantage of the newly available space. See Chapter 2, Resizing File Systems for details.
-
lvreduce -L SIZE /dev/VG_NAME/LV_NAME
Reduces the size of a specified logical volume.
Ensure that you reduce the size of the file system first before shrinking the volume, otherwise you risk losing data. See Chapter 2, Resizing File Systems for details.
-
lvrename /dev/VG_NAME/LV_NAME /dev/VG_NAME/NEW_LV_NAME
Renames an existing LVM logical volume. It does not change the volume group name.
In case you want to manage LV device nodes and symbolic links by using LVM instead of by using udev rules, you can achieve this by disabling notifications from udev with one of the following methods:
Configure
activation/udev_rules = 0
andactivation/udev_sync = 0
in/etc/lvm/lvm.conf
.Note that specifying
--nodevsync
with thelvcreate
command has the same effect asactivation/udev_sync = 0
; settingactivation/udev_rules = 0
is still required.Setting the environment variable
DM_DISABLE_UDEV
:export DM_DISABLE_UDEV=1
This will also disable notifications from udev. In addition, all udev related settings from
/etc/lvm/lvm.conf
will be ignored.
5.9.1 Resizing a Logical Volume with Commands #
The lvresize
, lvextend
, and
lvreduce
commands are used to resize logical volumes.
See the man pages for each of these commands for syntax and options
information. To extend an LV there must be enough unallocated space
available on the VG.
The recommended way to grow or shrink a logical volume is to use the YaST Partitioner. When using YaST, the size of the file system in the volume will automatically be adjusted, too.
LVs can be extended or shrunk manually while they are being used, but this may not be true for a file system on them. Extending or shrinking the LV does not automatically modify the size of file systems in the volume. You must use a different command to grow the file system afterward. For information about resizing file systems, see Chapter 2, Resizing File Systems.
Ensure that you use the right sequence when manually resizing an LV:
If you extend an LV, you must extend the LV before you attempt to grow the file system.
If you shrink an LV, you must shrink the file system before you attempt to shrink the LV.
To extend the size of a logical volume:
Open a terminal.
If the logical volume contains an Ext2 or Ext4 file system, which do not support online growing, dismount it. In case it contains file systems that are hosted for a virtual machine (such as a Xen VM), shut down the VM first.
At the terminal prompt, enter the following command to grow the size of the logical volume:
>
sudo
lvextend -L +SIZE /dev/VG_NAME/LV_NAMEFor SIZE, specify the amount of space you want to add to the logical volume, such as 10 GB. Replace
/dev/VG_NAME/LV_NAME
with the Linux path to the logical volume, such as/dev/LOCAL/DATA
. For example:>
sudo
lvextend -L +10GB /dev/vg1/v1Adjust the size of the file system. See Chapter 2, Resizing File Systems for details.
In case you have dismounted the file system, mount it again.
For example, to extend an LV with a (mounted and active) Btrfs on it by 10 GB:
>
sudo
lvextend −L +10G /dev/LOCAL/DATA>
sudo
btrfs filesystem resize +10G /dev/LOCAL/DATA
To shrink the size of a logical volume:
Open a terminal.
If the logical volume does not contain a Btrfs file system, dismount it. In case it contains file systems that are hosted for a virtual machine (such as a Xen VM), shut down the VM first. Note that volumes with the XFS file system cannot be reduced in size.
Adjust the size of the file system. See Chapter 2, Resizing File Systems for details.
At the terminal prompt, enter the following command to shrink the size of the logical volume to the size of the file system:
>
sudo
lvreduce /dev/VG_NAME/LV_NAMEIn case you have unmounted the file system, mount it again.
For example, to shrink an LV with a Btrfs on it by 5 GB:
>
sudo
btrfs filesystem resize -size 5G /dev/LOCAL/DATA sudo lvreduce /dev/LOCAL/DATA
Starting with SUSE Linux Enterprise Server 12 SP1, lvextend
,
lvresize
, and lvreduce
support the
option --resizefs
which will not only change the size of
the volume, but will also resize the file system. Therefore the examples
for lvextend
and lvreduce
shown
above can alternatively be run as follows:
>
sudo
lvextend --resizefs −L +10G /dev/LOCAL/DATA>
sudo
lvreduce --resizefs -L -5G /dev/LOCAL/DATA
Note that the --resizefs
is supported for the following
file systems: ext2/3/4, Btrfs, XFS. Resizing Btrfs with this option is
currently only available on SUSE Linux Enterprise Server, since it is not yet accepted
upstream.
5.9.2 Using LVM Cache Volumes #
LVM supports the use of fast block devices (such as an SSD device) as write-back or write-through caches for large slower block devices. The cache logical volume type uses a small and fast LV to improve the performance of a large and slow LV.
To set up LVM caching, you need to create two logical volumes on the caching device. A large one is used for the caching itself, a smaller volume is used to store the caching metadata. These two volumes need to be part of the same volume group as the original volume. When these volumes are created, they need to be converted into a cache pool which needs to be attached to the original volume:
Create the original volume (on a slow device) if not already existing.
Add the physical volume (from a fast device) to the same volume group the original volume is part of and create the cache data volume on the physical volume.
Create the cache metadata volume. The size should be 1/1000 of the size of the cache data volume, with a minimum size of 8 MB.
Combine the cache data volume and metadata volume into a cache pool volume:
>
sudo
lvconvert --type cache-pool --poolmetadata VOLUME_GROUP/METADATA_VOLUME VOLUME_GROUP/CACHING_VOLUMEAttach the cache pool to the original volume:
>
sudo
lvconvert --type cache --cachepool VOLUME_GROUP/CACHING_VOLUME VOLUME_GROUP/ORIGINAL_VOLUME
For more information on LVM caching, see the lvmcache(7) man page.
5.10 Tagging LVM2 Storage Objects #
A tag is an unordered keyword or term assigned to the metadata of a storage object. Tagging allows you to classify collections of LVM storage objects in ways that you find useful by attaching an unordered list of tags to their metadata.
5.10.1 Using LVM2 Tags #
After you tag the LVM2 storage objects, you can use the tags in commands to accomplish the following tasks:
Select LVM objects for processing according to the presence or absence of specific tags.
Use tags in the configuration file to control which volume groups and logical volumes are activated on a server.
Override settings in a global configuration file by specifying tags in the command.
A tag can be used in place of any command line LVM object reference that accepts:
a list of objects
a single object as long as the tag expands to a single object
Replacing the object name with a tag is not supported everywhere yet. After the arguments are expanded, duplicate arguments in a list are resolved by removing the duplicate arguments, and retaining the first instance of each argument.
Wherever there might be ambiguity of argument type, you must prefix a tag
with the commercial at sign (@) character, such as
@mytag
. Elsewhere, using the “@” prefix is
optional.
5.10.2 Requirements for Creating LVM2 Tags #
Consider the following requirements when using tags with LVM:
- Supported Characters
An LVM tag word can contain the ASCII uppercase characters A to Z, lowercase characters a to z, numbers 0 to 9, underscore (_), plus (+), hyphen (-), and period (.). The word cannot begin with a hyphen. The maximum length is 128 characters.
- Supported Storage Objects
You can tag LVM2 physical volumes, volume groups, logical volumes, and logical volume segments. PV tags are stored in its volume group’s metadata. Deleting a volume group also deletes the tags in the orphaned physical volume. Snapshots cannot be tagged, but their origin can be tagged.
LVM1 objects cannot be tagged because the disk format does not support it.
5.10.3 Command Line Tag Syntax #
--addtag
TAG_INFOAdd a tag to (or tag) an LVM2 storage object. Example:
>
sudo
vgchange --addtag @db1 vg1--deltag
TAG_INFORemove a tag from (or untag) an LVM2 storage object. Example:
>
sudo
vgchange --deltag @db1 vg1--tag
TAG_INFOSpecify the tag to use to narrow the list of volume groups or logical volumes to be activated or deactivated.
Enter the following to activate the volume if it has a tag that matches the tag provided (example):
>
sudo
lvchange -ay --tag @db1 vg1/vol2
5.10.4 Configuration File Syntax #
The following sections show example configurations for certain use cases.
5.10.4.1 Enabling Host Name Tags in the lvm.conf
File #
Add the following code to the /etc/lvm/lvm.conf
file
to enable host tags that are defined separately on host in a
/etc/lvm/lvm_<HOSTNAME>.conf
file.
tags { # Enable hostname tags hosttags = 1 }
You place the activation code in the
/etc/lvm/lvm_<HOSTNAME>.conf
file on the host. See
Section 5.10.4.3, “Defining Activation”.
5.10.4.2 Defining Tags for Host Names in the lvm.conf File #
tags { tag1 { } # Tag does not require a match to be set. tag2 { # If no exact match, tag is not set. host_list = [ "hostname1", "hostname2" ] } }
5.10.4.3 Defining Activation #
You can modify the /etc/lvm/lvm.conf
file to activate
LVM logical volumes based on tags.
In a text editor, add the following code to the file:
activation { volume_list = [ "vg1/lvol0", "@database" ] }
Replace @database
with your tag. Use
"@*"
to match the tag against any tag set on the host.
The activation command matches against VGNAME, VGNAME/LVNAME, or @TAG set in the metadata of volume groups and logical volumes. A volume group or logical volume is activated only if a metadata tag matches. The default if there is no match, is not to activate.
If volume_list
is not present and tags are defined on
the host, then it activates the volume group or logical volumes only if a
host tag matches a metadata tag.
If volume_list
is defined, but empty, and no tags are
defined on the host, then it does not activate.
If volume_list is undefined, it imposes no limits on LV activation (all are allowed).
5.10.4.4 Defining Activation in Multiple Host Name Configuration Files #
You can use the activation code in a host’s configuration file
(/etc/lvm/lvm_<HOST_TAG>.conf
)
when host tags are enabled in the lvm.conf
file. For
example, a server has two configuration files in the
/etc/lvm/
directory:
lvm.conf
|
lvm_<HOST_TAG>.conf
|
At start-up, load the /etc/lvm/lvm.conf
file, and
process any tag settings in the file. If any host tags were defined, it
loads the related
/etc/lvm/lvm_<HOST_TAG>.conf
file. When it searches for a specific configuration file entry, it
searches the host tag file first, then the lvm.conf
file, and stops at the first match. Within the
lvm_<HOST_TAG>.conf
file, use the reverse order that tags were set in. This allows the file
for the last tag set to be searched first. New tags set in the host tag
file will trigger additional configuration file loads.
5.10.5 Using Tags for a Simple Activation Control in a Cluster #
You can set up a simple host name activation control by enabling the
hostname_tags
option in the
/etc/lvm/lvm.conf
file. Use the same file on every
machine in a cluster so that it is a global setting.
In a text editor, add the following code to the
/etc/lvm/lvm.conf
file:tags { hostname_tags = 1 }
Replicate the file to all hosts in the cluster.
From any machine in the cluster, add
db1
to the list of machines that activatevg1/lvol2
:>
sudo
lvchange --addtag @db1 vg1/lvol2On the
db1
server, enter the following to activate it:>
sudo
lvchange -ay vg1/vol2
5.10.6 Using Tags to Activate On Preferred Hosts in a Cluster #
The examples in this section demonstrate two methods to accomplish the following:
Activate volume group
vg1
only on the database hostsdb1
anddb2
.Activate volume group
vg2
only on the file server hostfs1
.Activate nothing initially on the file server backup host
fsb1
, but be prepared for it to take over from the file server hostfs1
.
5.10.6.1 Option 1: Centralized Admin and Static Configuration Replicated Between Hosts #
In the following solution, the single configuration file is replicated among multiple hosts.
Add the
@database
tag to the metadata of volume groupvg1
. In a terminal, enter>
sudo
vgchange --addtag @database vg1Add the
@fileserver
tag to the metadata of volume groupvg2
. In a terminal, enter>
sudo
vgchange --addtag @fileserver vg2In a text editor, modify the
/etc/lvm/lvm.conf
file with the following code to define the@database
,@fileserver
,@fileserverbackup
tags.tags { database { host_list = [ "db1", "db2" ] } fileserver { host_list = [ "fs1" ] } fileserverbackup { host_list = [ "fsb1" ] } } activation { # Activate only if host has a tag that matches a metadata tag volume_list = [ "@*" ] }
Replicate the modified
/etc/lvm/lvm.conf
file to the four hosts:db1
,db2
,fs1
, andfsb1
.If the file server host goes down,
vg2
can be brought up onfsb1
by entering the following commands in a terminal on any node:>
sudo
vgchange --addtag @fileserverbackup vg2>
sudo
vgchange -ay vg2
5.10.6.2 Option 2: Localized Admin and Configuration #
In the following solution, each host holds locally the information about which classes of volume to activate.
Add the
@database
tag to the metadata of volume groupvg1
. In a terminal, enter>
sudo
vgchange --addtag @database vg1Add the
@fileserver
tag to the metadata of volume groupvg2
. In a terminal, enter>
sudo
vgchange --addtag @fileserver vg2Enable host tags in the
/etc/lvm/lvm.conf
file:In a text editor, modify the
/etc/lvm/lvm.conf
file with the following code to enable host tag configuration files.tags { hosttags = 1 }
Replicate the modified
/etc/lvm/lvm.conf
file to the four hosts:db1
,db2
,fs1
, andfsb1
.
On host
db1
, create an activation configuration file for the database hostdb1
. In a text editor, create/etc/lvm/lvm_db1.conf
file and add the following code:activation { volume_list = [ "@database" ] }
On host
db2
, create an activation configuration file for the database hostdb2
. In a text editor, create/etc/lvm/lvm_db2.conf
file and add the following code:activation { volume_list = [ "@database" ] }
On host fs1, create an activation configuration file for the file server host
fs1
. In a text editor, create/etc/lvm/lvm_fs1.conf
file and add the following code:activation { volume_list = [ "@fileserver" ] }
If the file server host
fs1
goes down, to bring up a spare file server host fsb1 as a file server:On host
fsb1
, create an activation configuration file for the hostfsb1
. In a text editor, create/etc/lvm/lvm_fsb1.conf
file and add the following code:activation { volume_list = [ "@fileserver" ] }
In a terminal, enter one of the following commands:
>
sudo
vgchange -ay vg2>
sudo
vgchange -ay @fileserver
6 LVM Volume Snapshots #
A Logical Volume Manager (LVM) logical volume snapshot is a copy-on-write technology that monitors changes to an existing volume’s data blocks so that when a write is made to one of the blocks, the block’s value at the snapshot time is copied to a snapshot volume. In this way, a point-in-time copy of the data is preserved until the snapshot volume is deleted.
6.1 Understanding Volume Snapshots #
A file system snapshot contains metadata about itself and data blocks from a source logical volume that has changed since the snapshot was taken. When you access data via the snapshot, you see a point-in-time copy of the source logical volume. There is no need to restore data from backup media or to overwrite the changed data.
During the snapshot’s lifetime, the snapshot must be mounted before its source logical volume can be mounted.
LVM volume snapshots allow you to create a backup from a point-in-time view of the file system. The snapshot is created instantly and persists until you delete it. You can back up the file system from the snapshot while the volume itself continues to be available for users. The snapshot initially contains some metadata about the snapshot, but no actual data from the source logical volume. Snapshot uses copy-on-write technology to detect when data changes in an original data block. It copies the value it held when the snapshot was taken to a block in the snapshot volume, then allows the new data to be stored in the source block. As more blocks change from their original value on the source logical volume, the snapshot size grows.
When you are sizing the snapshot, consider how much data is expected to change on the source logical volume and how long you plan to keep the snapshot. The amount of space that you allocate for a snapshot volume can vary, depending on the size of the source logical volume, how long you plan to keep the snapshot, and the number of data blocks that are expected to change during the snapshot’s lifetime. The snapshot volume cannot be resized after it is created. As a guide, create a snapshot volume that is about 10% of the size of the original logical volume. If you anticipate that every block in the source logical volume will change at least one time before you delete the snapshot, then the snapshot volume should be at least as large as the source logical volume plus some additional space for metadata about the snapshot volume. Less space is required if the data changes infrequently or if the expected lifetime is sufficiently brief.
In LVM2, snapshots are read/write by default. When you write data directly to the snapshot, that block is marked in the exception table as used, and never gets copied from the source logical volume. You can mount the snapshot volume, and test application changes by writing data directly to the snapshot volume. You can easily discard the changes by dismounting the snapshot, removing the snapshot, and then remounting the source logical volume.
In a virtual guest environment, you can use the snapshot function for LVM logical volumes you create on the server’s disks, as you would on a physical server.
In a virtual host environment, you can use the snapshot function to back up the virtual machine’s storage back-end, or to test changes to a virtual machine image, such as for patches or upgrades, without modifying the source logical volume. The virtual machine must be using an LVM logical volume as its storage back-end, as opposed to using a virtual disk file. You can mount the LVM logical volume and use it to store the virtual machine image as a file-backed disk, or you can assign the LVM logical volume as a physical disk to write to it as a block device.
Beginning in SLES 11 SP3, an LVM logical volume snapshot can be thinly provisioned. Thin provisioning is assumed if you create a snapshot without a specified size. The snapshot is created as a thin volume that uses space as needed from a thin pool. A thin snapshot volume has the same characteristics as any other thin volume. You can independently activate the volume, extend the volume, rename the volume, remove the volume, and even snapshot the volume.
To use thinly provisioned snapshots in a cluster, the source logical volume and its snapshots must be managed in a single cluster resource. This allows the volume and its snapshots to always be mounted exclusively on the same node.
When you are done with the snapshot, it is important to remove it from the system. A snapshot eventually fills up completely as data blocks change on the source logical volume. When the snapshot is full, it is disabled, which prevents you from remounting the source logical volume.
If you create multiple snapshots for a source logical volume, remove the snapshots in a last created, first deleted order.
6.2 Creating Linux Snapshots with LVM #
The Logical Volume Manager (LVM) can be used for creating snapshots of your file system.
Open a terminal and enter
>
sudo
lvcreate -s [-L <size>] -n SNAP_VOLUME SOURCE_VOLUME_PATH
If no size is specified, the snapshot is created as a thin snapshot.
For example:
>
sudo
lvcreate -s -L 1G -n linux01-snap /dev/lvm/linux01
The snapshot is created as the /dev/lvm/linux01-snap
volume.
6.3 Monitoring a Snapshot #
Open a terminal and enter
>
sudo
lvdisplay SNAP_VOLUME
For example:
>
sudo
lvdisplay /dev/vg01/linux01-snap --- Logical volume --- LV Name /dev/lvm/linux01 VG Name vg01 LV UUID QHVJYh-PR3s-A4SG-s4Aa-MyWN-Ra7a-HL47KL LV Write Access read/write LV snapshot status active destination for /dev/lvm/linux01 LV Status available # open 0 LV Size 80.00 GB Current LE 1024 COW-table size 8.00 GB COW-table LE 512 Allocated to snapshot 30% Snapshot chunk size 8.00 KB Segments 1 Allocation inherit Read ahead sectors 0 Block device 254:5
6.4 Deleting Linux Snapshots #
Open a terminal and enter
>
sudo
lvremove SNAP_VOLUME_PATH
For example:
>
sudo
lvremove /dev/lvmvg/linux01-snap
6.5 Using Snapshots for Virtual Machines on a Virtual Host #
Using an LVM logical volume for a virtual machine’s back-end storage allows flexibility in administering the underlying device, such as making it easier to move storage objects, create snapshots, and back up data. You can mount the LVM logical volume and use it to store the virtual machine image as a file-backed disk, or you can assign the LVM logical volume as a physical disk to write to it as a block device. You can create a virtual disk image on the LVM logical volume, then snapshot the LVM.
You can leverage the read/write capability of the snapshot to create different instances of a virtual machine, where the changes are made to the snapshot for a particular virtual machine instance. You can create a virtual disk image on an LVM logical volume, snapshot the source logical volume, and modify the snapshot for a particular virtual machine instance. You can create another snapshot of the source logical volume, and modify it for a different virtual machine instance. The majority of the data for the different virtual machine instances resides with the image on the source logical volume.
You can also leverage the read/write capability of the snapshot to preserve the virtual disk image while testing patches or upgrades in the guest environment. You create a snapshot of the LVM volume that contains the image, and then run the virtual machine on the snapshot location. The source logical volume is unchanged, and all changes for that machine are written to the snapshot. To return to the source logical volume of the virtual machine image, you power off the virtual machine, then remove the snapshot from the source logical volume. To start over, you re-create the snapshot, mount the snapshot, and restart the virtual machine on the snapshot image.
The following procedure uses a file-backed virtual disk image and the Xen hypervisor. You can adapt the procedure in this section for other hypervisors that run on the SUSE Linux Enterprise platform, such as KVM. To run a file-backed virtual machine image from the snapshot volume:
Ensure that the source logical volume that contains the file-backed virtual machine image is mounted, such as at mount point
/var/lib/xen/images/<IMAGE_NAME>
.Create a snapshot of the LVM logical volume with enough space to store the differences that you expect.
>
sudo
lvcreate -s -L 20G -n myvm-snap /dev/lvmvg/myvmIf no size is specified, the snapshot is created as a thin snapshot.
Create a mount point where you will mount the snapshot volume.
>
sudo
mkdir -p /mnt/xen/vm/myvm-snapMount the snapshot volume at the mount point you created.
>
sudo
mount -t auto /dev/lvmvg/myvm-snap /mnt/xen/vm/myvm-snapIn a text editor, copy the configuration file for the source virtual machine, modify the paths to point to the file-backed image file on the mounted snapshot volume, and save the file such as
/etc/xen/myvm-snap.cfg
.Start the virtual machine using the mounted snapshot volume of the virtual machine.
>
sudo
xm create -c /etc/xen/myvm-snap.cfg(Optional) Remove the snapshot, and use the unchanged virtual machine image on the source logical volume.
>
sudo
umount /mnt/xenvms/myvm-snap>
sudo
lvremove -f /dev/lvmvg/mylvm-snap(Optional) Repeat this process as desired.
6.6 Merging a Snapshot with the Source Logical Volume to Revert Changes or Roll Back to a Previous State #
Snapshots can be useful if you need to roll back or restore data on a volume to a previous state. For example, you might need to revert data changes that resulted from an administrator error or a failed or undesirable package installation or upgrade.
You can use the lvconvert --merge
command to revert the
changes made to an LVM logical volume. The merging begins as follows:
If both the source logical volume and snapshot volume are not open, the merge begins immediately.
If the source logical volume or snapshot volume are open, the merge starts the first time either the source logical volume or snapshot volume are activated and both are closed.
If the source logical volume cannot be closed, such as the root file system, the merge is deferred until the next time the server reboots and the source logical volume is activated.
If the source logical volume contains a virtual machine image, you must shut down the virtual machine, deactivate the source logical volume and snapshot volume (by dismounting them in that order), and then issue the merge command. Because the source logical volume is automatically remounted and the snapshot volume is deleted when the merge is complete, you should not restart the virtual machine until after the merge is complete. After the merge is complete, you use the resulting logical volume for the virtual machine.
After a merge begins, the merge continues automatically after server restarts until it is complete. A new snapshot cannot be created for the source logical volume while a merge is in progress.
While the merge is in progress, reads or writes to the source logical volume are transparently redirected to the snapshot that is being merged. This allows users to immediately view and access the data as it was when the snapshot was created. They do not need to wait for the merge to complete.
When the merge is complete, the source logical volume contains the same data as it did when the snapshot was taken, plus any data changes made after the merge began. The resulting logical volume has the source logical volume’s name, minor number, and UUID. The source logical volume is automatically remounted, and the snapshot volume is removed.
Open a terminal and enter
>
sudo
lvconvert --merge [-b] [-i SECONDS] [SNAP_VOLUME_PATH[...snapN]|@VOLUME_TAG]You can specify one or multiple snapshots on the command line. You can alternatively tag multiple source logical volumes with the same volume tag then specify
@<VOLUME_TAG>
on the command line. The snapshots for the tagged volumes are merged to their respective source logical volumes. For information about tagging logical volumes, see Section 5.10, “Tagging LVM2 Storage Objects”.The options include:
- -b, --background
Run the daemon in the background. This allows multiple specified snapshots to be merged concurrently in parallel.
- -i, --interval <SECONDS>
Report progress as a percentage at regular intervals. Specify the interval in seconds.
For more information about this command, see the
lvconvert(8)
man page.For example:
>
sudo
lvconvert --merge /dev/lvmvg/linux01-snapThis command merges
/dev/lvmvg/linux01-snap
into its source logical volume.>
sudo
lvconvert --merge @mytagIf
lvol1
,lvol2
, andlvol3
are all tagged withmytag
, each snapshot volume is merged serially with its respective source logical volume; that is:lvol1
, thenlvol2
, thenlvol3
. If the--background
option is specified, the snapshots for the respective tagged logical volume are merged concurrently in parallel.(Optional) If both the source logical volume and snapshot volume are open and they can be closed, you can manually deactivate and activate the source logical volume to get the merge to start immediately.
>
sudo
umount ORIGINAL_VOLUME>
sudo
lvchange -an ORIGINAL_VOLUME>
sudo
lvchange -ay ORIGINAL_VOLUME>
sudo
mount ORIGINAL_VOLUME MOUNT_POINTFor example:
>
sudo
umount /dev/lvmvg/lvol01>
sudo
lvchange -an /dev/lvmvg/lvol01>
sudo
lvchange -ay /dev/lvmvg/lvol01>
sudo
mount /dev/lvmvg/lvol01 /mnt/lvol01(Optional) If both the source logical volume and snapshot volume are open and the source logical volume cannot be closed, such as the
root
file system, you can restart the server and mount the source logical volume to get the merge to start immediately after the restart.
Part III Software RAID #
- 7 Software RAID Configuration
The purpose of RAID (redundant array of independent disks) is to combine several hard disk partitions into one large virtual hard disk to optimize performance, data security, or both. Most RAID controllers use the SCSI protocol because it can address a larger number of hard disks in a more effective…
- 8 Configuring Software RAID for the Root Partition
In SUSE Linux Enterprise Server, the Device Mapper RAID tool has been integrated into the YaST Partitioner. You can use the partitioner at install time to create a software RAID for the system device that contains your root (/) partition. The /boot partition cannot be stored on a RAID partition unle…
- 9 Creating Software RAID 10 Devices
This section describes how to set up nested and complex RAID 10 devices. A RAID 10 device consists of nested RAID 1 (mirroring) and RAID 0 (striping) arrays. Nested RAIDs can either be set up as striped mirrors (RAID 1+0) or as mirrored stripes (RAID 0+1). A complex RAID 10 setup also combines mirro…
- 10 Creating a Degraded RAID Array
A degraded array is one in which some devices are missing. Degraded arrays are supported only for RAID 1, RAID 4, RAID 5, and RAID 6. These RAID types are designed to withstand some missing devices as part of their fault-tolerance features. Typically, degraded arrays occur when a device fails. It is possible to create a degraded array on purpose.
- 11 Resizing Software RAID Arrays with mdadm
This section describes how to increase or reduce the size of a software RAID 1, 4, 5, or 6 device with the Multiple Device Administration (
mdadm(8)
) tool.- 12 Storage Enclosure LED Utilities for MD Software RAIDs
Storage enclosure LED Monitoring utility (
ledmon
) and LED Control (ledctl
) utility are Linux user space applications that use a broad range of interfaces and protocols to control storage enclosure LEDs. The primary usage is to visualize the status of Linux MD software RAID devices created with the mdadm utility. Theledmon
daemon monitors the status of the drive array and updates the status of the drive LEDs. Theledctl
utility allows you to set LED patterns for specified devices.- 13 Toubleshooting software RAIDs
Check the /proc/mdstat file to find out whether a RAID partition has been damaged. If a disk fails, replace the defective hard disk with a new one partitioned the same way. Then restart your system and enter the command mdadm /dev/mdX --add /dev/sdX. Replace X with your particular device identifiers…
7 Software RAID Configuration #
The purpose of RAID (redundant array of independent disks) is to combine several hard disk partitions into one large virtual hard disk to optimize performance, data security, or both. Most RAID controllers use the SCSI protocol because it can address a larger number of hard disks in a more effective way than the IDE protocol and is more suitable for parallel processing of commands. There are some RAID controllers that support IDE or SATA hard disks. Software RAID provides the advantages of RAID systems without the additional cost of hardware RAID controllers. However, this requires some CPU time and has memory requirements that make it unsuitable for real high performance computers.
Software RAID underneath clustered file systems needs to be set up using a cluster multi-device (Cluster MD). Refer to the Administration Guide for SUSE Linux Enterprise High Availability.
SUSE Linux Enterprise offers the option of combining several hard disks into one soft RAID system. RAID implies several strategies for combining several hard disks in a RAID system, each with different goals, advantages, and characteristics. These variations are commonly known as RAID levels.
7.1 Understanding RAID Levels #
This section describes common RAID levels 0, 1, 2, 3, 4, 5, and nested RAID levels.
7.1.1 RAID 0 #
This level improves the performance of your data access by spreading out blocks of each file across multiple disks. Actually, this is not a RAID, because it does not provide data backup, but the name RAID 0 for this type of system has become the norm. With RAID 0, two or more hard disks are pooled together. The performance is very good, but the RAID system is destroyed and your data lost if even one hard disk fails.
7.1.2 RAID 1 #
This level provides adequate security for your data, because the data is copied to another hard disk 1:1. This is known as hard disk mirroring. If a disk is destroyed, a copy of its contents is available on another mirrored disk. All disks except one could be damaged without endangering your data. However, if damage is not detected, damaged data might be mirrored to the correct disk and the data is corrupted that way. The writing performance suffers a little in the copying process compared to when using single disk access (10 to 20 percent slower), but read access is significantly faster in comparison to any one of the normal physical hard disks, because the data is duplicated so can be scanned in parallel. RAID 1 generally provides nearly twice the read transaction rate of single disks and almost the same write transaction rate as single disks.
7.1.3 RAID 2 and RAID 3 #
These are not typical RAID implementations. Level 2 stripes data at the bit level rather than the block level. Level 3 provides byte-level striping with a dedicated parity disk and cannot service simultaneous multiple requests. Both levels are rarely used.
7.1.4 RAID 4 #
Level 4 provides block-level striping like Level 0 combined with a dedicated parity disk. If a data disk fails, the parity data is used to create a replacement disk. However, the parity disk might create a bottleneck for write access. Nevertheless, Level 4 is sometimes used.
7.1.5 RAID 5 #
RAID 5 is an optimized compromise between Level 0 and Level 1 in terms of performance and redundancy. The hard disk space equals the number of disks used minus one. The data is distributed over the hard disks as with RAID 0. Parity blocks, created on one of the partitions, are there for security reasons. They are linked to each other with XOR, enabling the contents to be reconstructed by the corresponding parity block in case of system failure. With RAID 5, no more than one hard disk can fail at the same time. If one hard disk fails, it must be replaced when possible to avoid the risk of losing data.
7.1.6 RAID 6 #
RAID 6 is an extension of RAID 5 that allows for additional fault tolerance by using a second independent distributed parity scheme (dual parity). Even if two of the hard disks fail during the data recovery process, the system continues to be operational, with no data loss.
RAID 6 provides for extremely high data fault tolerance by sustaining multiple simultaneous drive failures. It handles the loss of any two devices without data loss. Accordingly, it requires N+2 drives to store N drives worth of data. It requires a minimum of four devices.
The performance for RAID 6 is slightly lower but comparable to RAID 5 in normal mode and single disk failure mode. It is very slow in dual disk failure mode. A RAID 6 configuration needs a considerable amount of CPU time and memory for write operations.
Feature |
RAID 5 |
RAID 6 |
---|---|---|
Number of devices |
N+1, minimum of 3 |
N+2, minimum of 4 |
Parity |
Distributed, single |
Distributed, dual |
Performance |
Medium impact on write and rebuild |
More impact on sequential write than RAID 5 |
Fault-tolerance |
Failure of one component device |
Failure of two component devices |
7.1.7 Nested and Complex RAID Levels #
Other RAID levels have been developed, such as RAIDn, RAID 10, RAID 0+1, RAID 30, and RAID 50. Some are proprietary implementations created by hardware vendors. Examples for creating RAID 10 configurations can be found in Chapter 9, Creating Software RAID 10 Devices.
7.2 Soft RAID Configuration with YaST #
The YaST soft RAID configuration can be reached from the YaST Expert Partitioner. This partitioning tool also enables you to edit and delete existing partitions and create new ones that should be used with soft RAID. These instructions apply on setting up RAID levels 0, 1, 5, and 6. Setting up RAID 10 configurations is explained in Chapter 9, Creating Software RAID 10 Devices.
Launch YaST and open the
.If necessary, create partitions that should be used with your RAID configuration. Do not format them and set the partition type to Book “Deployment Guide”, Chapter 10 “Expert Partitioner”, Section 10.1 “Using the Expert Partitioner” for details.
. When using existing partitions it is not necessary to change their partition type—YaST will automatically do so. Refer toIt is strongly recommended to use partitions stored on different hard disks to decrease the risk of losing data if one is defective (RAID 1 and 5) and to optimize the performance of RAID 0.
For RAID 0 at least two partitions are needed. RAID 1 requires exactly two partitions, while at least three partitions are required for RAID 5. A RAID 6 setup requires at least four partitions. It is recommended to use only partitions of the same size because each segment can contribute only the same amount of space as the smallest sized partition.
In the left panel, select
.A list of existing RAID configurations opens in the right panel.
At the lower left of the RAID page, click
.Select a
and an appropriate number of partitions from the dialog.You can optionally assign a
to your RAID. It will make it available as/dev/md/NAME
. See Section 7.2.1, “RAID Names” for more information.Figure 7.1: Example RAID 5 Configuration #Proceed with
.Select the https://raid.wiki.kernel.org/index.php/RAID_setup#Chunk_sizes for more information. More information on parity algorithms can be found with
and, if applicable, the . The optimal chunk size depends on the type of data and the type of RAID. Seeman 8 mdadm
when searching for the--layout
option. If unsure, stick with the defaults.Choose a
for the volume. Your choice here only affects the default values for the upcoming dialog. They can be changed in the next step. If in doubt, choose .Under
, select , then select the . The content of the menu depends on the file system. Usually there is no need to change the defaults.Under
, select , then select the mount point. Click to add special mounting options for the volume.Click
.Click
, verify that the changes are listed, then click .
While the partitioner makes it possible to create a RAID on top of disks instead of partitions, we do not recommend this approach for a number of reasons. Installing a bootloader on such RAID is not supported, so you need to use a separate device for booting. Tools like fdisk and parted do not work properly with such RAIDs, which may lead to incorrect diagnosis and actions by a person who is unaware of the RAID's particular setup.
7.2.1 RAID Names #
By default, software RAID devices have numeric names following the pattern
mdN
, where N
is a number. As such
they can be accessed as, for example, /dev/md127
and
are listed as md127
in /proc/mdstat
and /proc/partitions
. Working with these names can be
clumsy. SUSE Linux Enterprise Server offers two ways to work around this problem:
- Providing a Named Link to the Device
You can optionally specify a name for the RAID device when creating it with YaST or on the command line with
mdadm --create '/dev/md/
NAME'. The device name will still bemdN
, but a link/dev/md/NAME
will be created:>
ls -og /dev/md total 0 lrwxrwxrwx 1 8 Dec 9 15:11 myRAID -> ../md127The device will still be listed as
md127
under/proc
.- Providing a Named Device
In case a named link to the device is not sufficient for your setup, add the line CREATE names=yes to
/etc/mdadm.conf
by running the following command:>
echo "CREATE names=yes" | sudo tee -a /etc/mdadm.confIt will cause names like
myRAID
to be used as a “real” device name. The device will not only be accessible at/dev/myRAID
, but also be listed asmyRAID
under/proc
. Note that this will only apply to RAIDs configured after the change to the configuration file. Active RAIDS will continue to use themdN
names until they get stopped and re-assembled.Warning: Incompatible ToolsNot all tools may support named RAID devices. In case a tool expects a RAID device to be named
mdN
, it will fail to identify the devices.
7.3 Monitoring software RAIDs #
You can run mdadm
as a daemon in the monitor
mode to monitor your software RAID. In the monitor
mode mdadm
performs regular checks on the array for disk failures. If there is a failure, mdadm
sends an email to the administrator. To define the time interval of the checks, run the following command:
mdadm --monitor --mail=root@localhost --delay=1800 /dev/md2
The command above turns on monitoring of the /dev/md2
array in intervals of 1800s. In case of a failure, an email to root@localhost
will be send.
The RAID checks are enabled by default. It may happen that the interval between each check is not long enough and you may encounter warnings. Thus you can increase the interval by setting higher value by the delay
option.
7.4 For More Information #
Configuration instructions and more details for soft RAID can be found in the HOWTOs at:
The Linux RAID wiki: https://raid.wiki.kernel.org/
The Software RAID HOWTO in the
/usr/share/doc/packages/mdadm/Software-RAID.HOWTO.html
file
Linux RAID mailing lists are also available, such as linux-raid at http://marc.info/?l=linux-raid.
8 Configuring Software RAID for the Root Partition #
In SUSE Linux Enterprise Server, the Device Mapper RAID tool has been integrated into the
YaST Partitioner. You can use the partitioner at install time to create a
software RAID for the system device that contains your root
(/
) partition. The /boot
partition
cannot be stored on a RAID partition unless it is RAID 1.
8.1 Prerequisites for Using a Software RAID Device for the Root Partition #
Ensure that your configuration meets the following requirements:
You need two hard disks to create the RAID 1 mirror device. The hard disks should be similarly sized. The RAID assumes the size of the smaller drive. The block storage devices can be any combination of local (in or directly attached to the machine), Fibre Channel storage subsystems, or iSCSI storage subsystems.
A separate partition for
/boot
is not required if you install the boot loader in the MBR. If installing the boot loader in the MBR is not an option,/boot
needs to reside on a separate partition.For UEFI machines, you need to set up a dedicated
/boot/efi
partition. It needs to be VFAT-formatted, and may reside on the RAID 1 device to prevent booting problems in case the physical disk with/boot/efi
fails.If you are using hardware RAID devices, do not attempt to run software RAIDs on top of it.
If you are using iSCSI target devices, you need to enable the iSCSI initiator support before you create the RAID device.
If your storage subsystem provides multiple I/O paths between the server and its directly attached local devices, Fibre Channel devices, or iSCSI devices that you want to use in the software RAID, you need to enable the multipath support before you create the RAID device.
8.2
Setting Up the System with a Software RAID Device for the Root
(/
) Partition
#
Start the installation with YaST and proceed as described in Book “Deployment Guide”, Chapter 8 “Installation Steps” until you reach the step.
Click
to open the custom partitioning tool. YaST makes a default proposal, you can use this proposal by clicking . You can also discard the suggested proposal by clicking .(Optional) If there are iSCSI target devices that you want to use, you need to enable the iSCSI Initiator software by choosing Chapter 15, Mass Storage over IP Networks: iSCSI for further details.
› from the lower right section of the screen. Refer to(Optional) You may need to configure multiple network interfaces for FCoE, click
to do so.(Optional) In case you have used the suggested proposal and you do not need it anymore. Click
to delete the proposed partitioning.Set up the
format for each of the devices you want to use for the software RAID. You should use RAID for/
,/boot/efi
, or swap partitions.In the left panel, select
and select the device you want to use. Click the tab and then click .Under
, specify the size to use, then click .Under
, choose .Select
and . Set the to .Click
and repeat these instructions for the second partition.
Create the RAID device for the
/
partition.In the left panel, select
and then .Set the desired
for the/
partition and the tosystem
.Select the two RAID devices you prepared in the previous step from the
section and them.Proceed with
.Under
, select the chunk size from the drop-down box. Sticking with the default is a safe choice.In the left panel, click
RAID
and then select thesystem
. Click .Under
, select and proceed with .Select the
and set the mount point to/
. Leave the dialog withNext
.
The software RAID device is managed by Device Mapper, and creates a device under the
/dev/md/system
path.Optionally for UEFI machines, use similar steps to create the
/boot/efi
mounted partition. Remember that only RAID 1 is supported for/boot/efi
, and the partition needs to be formatted with the FAT file system.Figure 8.1: , , and swap on RAIDs #Click
to leave the partitioner.The new proposal appears on the
page.Continue with the installation. For UEFI machines with a separate
/boot/efi
partition, click on the screen and set as the . Check that the option is activated.Whenever you reboot your server, Device Mapper is started at boot time so that the software RAID is automatically recognized, and the operating system on the root (/) partition can be started.
9 Creating Software RAID 10 Devices #
This section describes how to set up nested and complex RAID 10 devices. A RAID 10 device consists of nested RAID 1 (mirroring) and RAID 0 (striping) arrays. Nested RAIDs can either be set up as striped mirrors (RAID 1+0) or as mirrored stripes (RAID 0+1). A complex RAID 10 setup also combines mirrors and stripes and additional data security by supporting a higher data redundancy level.
9.1 Creating Nested RAID 10 Devices with mdadm
#
A nested RAID device consists of a RAID array that uses another RAID array
as its basic element, instead of using physical disks. The goal of this
configuration is to improve the performance and fault tolerance of the RAID.
Setting up nested RAID levels is not supported by YaST, but can be done by
using the mdadm
command line tool.
Based on the order of nesting, two different nested RAIDs can be set up. This document uses the following terminology:
RAID 1+0: RAID 1 (mirror) arrays are built first, then combined to form a RAID 0 (stripe) array.
RAID 0+1: RAID 0 (stripe) arrays are built first, then combined to form a RAID 1 (mirror) array.
The following table describes the advantages and disadvantages of RAID 10 nesting as 1+0 versus 0+1. It assumes that the storage objects you use reside on different disks, each with a dedicated I/O capability.
RAID Level |
Description |
Performance and Fault Tolerance |
---|---|---|
10 (1+0) |
RAID 0 (stripe) built with RAID 1 (mirror) arrays |
RAID 1+0 provides high levels of I/O performance, data redundancy, and disk fault tolerance. Because each member device in the RAID 0 is mirrored individually, multiple disk failures can be tolerated and data remains available as long as the disks that fail are in different mirrors. You can optionally configure a spare for each underlying mirrored array, or configure a spare to serve a spare group that serves all mirrors. |
10 (0+1) |
RAID 1 (mirror) built with RAID 0 (stripe) arrays |
RAID 0+1 provides high levels of I/O performance and data redundancy, but slightly less fault tolerance than a 1+0. If multiple disks fail on one side of the mirror, then the other mirror is available. However, if disks are lost concurrently on both sides of the mirror, all data is lost. This solution offers less disk fault tolerance than a 1+0 solution, but if you need to perform maintenance or maintain the mirror on a different site, you can take an entire side of the mirror offline and still have a fully functional storage device. Also, if you lose the connection between the two sites, either site operates independently of the other. That is not true if you stripe the mirrored segments, because the mirrors are managed at a lower level. If a device fails, the mirror on that side fails because RAID 1 is not fault-tolerant. Create a new RAID 0 to replace the failed side, then resynchronize the mirrors. |
9.1.1 Creating Nested RAID 10 (1+0) with mdadm #
A nested RAID 1+0 is built by creating two or more RAID 1 (mirror) devices, then using them as component devices in a RAID 0.
If you need to manage multiple connections to the devices, you must configure multipath I/O before configuring the RAID devices. For information, see Chapter 18, Managing Multipath I/O for Devices.
The procedure in this section uses the device names shown in the following table. Ensure that you modify the device names with the names of your own devices.
Raw Devices |
RAID 1 (mirror) |
RAID 1+0 (striped mirrors) | ||
---|---|---|---|---|
|
|
| ||
|
|
Open a terminal.
If necessary, create four 0xFD Linux RAID partitions of equal size using a disk partitioner such as parted.
Create two software RAID 1 devices, using two different devices for each device. At the command prompt, enter these two commands:
>
sudo
mdadm --create /dev/md0 --run --level=1 --raid-devices=2 /dev/sdb1 /dev/sdc1 sudo mdadm --create /dev/md1 --run --level=1 --raid-devices=2 /dev/sdd1 /dev/sde1Create the nested RAID 1+0 device. At the command prompt, enter the following command using the software RAID 1 devices you created in the previous step:
>
sudo
mdadm --create /dev/md2 --run --level=0 --chunk=64 \ --raid-devices=2 /dev/md0 /dev/md1The default chunk size is 64 KB.
Create a file system on the RAID 1+0 device
/dev/md2
, for example an XFS file system:>
sudo
mkfs.xfs /dev/md2Modify the command to use a different file system.
Edit the
/etc/mdadm.conf
file or create it, if it does not exist (for example by runningsudo vi /etc/mdadm.conf
). Add the following lines (if the file already exists, the first line probably already exists).DEVICE containers partitions ARRAY /dev/md0 UUID=UUID ARRAY /dev/md1 UUID=UUID ARRAY /dev/md2 UUID=UUID
The UUID of each device can be retrieved with the following command:
>
sudo
mdadm -D /dev/DEVICE | grep UUIDEdit the
/etc/fstab
file to add an entry for the RAID 1+0 device/dev/md2
. The following example shows an entry for a RAID device with the XFS file system and/data
as a mount point./dev/md2 /data xfs defaults 1 2
Mount the RAID device:
>
sudo
mount /data
9.1.2 Creating Nested RAID 10 (0+1) with mdadm #
A nested RAID 0+1 is built by creating two to four RAID 0 (striping) devices, then mirroring them as component devices in a RAID 1.
If you need to manage multiple connections to the devices, you must configure multipath I/O before configuring the RAID devices. For information, see Chapter 18, Managing Multipath I/O for Devices.
In this configuration, spare devices cannot be specified for the underlying RAID 0 devices because RAID 0 cannot tolerate a device loss. If a device fails on one side of the mirror, you must create a replacement RAID 0 device, than add it into the mirror.
The procedure in this section uses the device names shown in the following table. Ensure that you modify the device names with the names of your own devices.
Raw Devices |
RAID 0 (stripe) |
RAID 0+1 (mirrored stripes) | ||
---|---|---|---|---|
|
|
| ||
|
|
Open a terminal.
If necessary, create four 0xFD Linux RAID partitions of equal size using a disk partitioner such as parted.
Create two software RAID 0 devices, using two different devices for each RAID 0 device. At the command prompt, enter these two commands:
>
sudo
mdadm --create /dev/md0 --run --level=0 --chunk=64 \ --raid-devices=2 /dev/sdb1 /dev/sdc1 sudo mdadm --create /dev/md1 --run --level=0 --chunk=64 \ --raid-devices=2 /dev/sdd1 /dev/sde1The default chunk size is 64 KB.
Create the nested RAID 0+1 device. At the command prompt, enter the following command using the software RAID 0 devices you created in the previous step:
>
sudo
mdadm --create /dev/md2 --run --level=1 --raid-devices=2 /dev/md0 /dev/md1Create a file system on the RAID 1+0 device
/dev/md2
, for example an XFS file system:>
sudo
mkfs.xfs /dev/md2Modify the command to use a different file system.
Edit the
/etc/mdadm.conf
file or create it, if it does not exist (for example by runningsudo vi /etc/mdadm.conf
). Add the following lines (if the file exists, the first line probably already exists, too).DEVICE containers partitions ARRAY /dev/md0 UUID=UUID ARRAY /dev/md1 UUID=UUID ARRAY /dev/md2 UUID=UUID
The UUID of each device can be retrieved with the following command:
>
sudo
mdadm -D /dev/DEVICE | grep UUIDEdit the
/etc/fstab
file to add an entry for the RAID 1+0 device/dev/md2
. The following example shows an entry for a RAID device with the XFS file system and/data
as a mount point./dev/md2 /data xfs defaults 1 2
Mount the RAID device:
>
sudo
mount /data
9.2 Creating a Complex RAID 10 #
YaST (and mdadm
with the --level=10
option) creates a single complex software RAID 10 that combines
features of both RAID 0 (striping) and RAID 1 (mirroring). Multiple copies
of all data blocks are arranged on multiple drives following a striping
discipline. Component devices should be the same size.
The complex RAID 10 is similar in purpose to a nested RAID 10 (1+0), but differs in the following ways:
Feature |
Complex RAID 10 |
Nested RAID 10 (1+0) |
---|---|---|
Number of devices |
Allows an even or odd number of component devices |
Requires an even number of component devices |
Component devices |
Managed as a single RAID device |
Manage as a nested RAID device |
Striping |
Striping occurs in the near or far layout on component devices. The far layout provides sequential read throughput that scales by number of drives, rather than number of RAID 1 pairs. |
Striping occurs consecutively across component devices |
Multiple copies of data |
Two or more copies, up to the number of devices in the array |
Copies on each mirrored segment |
Hot spare devices |
A single spare can service all component devices |
Configure a spare for each underlying mirrored array, or configure a spare to serve a spare group that serves all mirrors. |
9.2.1 Number of Devices and Replicas in the Complex RAID 10 #
When configuring a complex RAID 10 array, you must specify the number of replicas of each data block that are required. The default number of replicas is two, but the value can be two to the number of devices in the array.
You must use at least as many component devices as the number of replicas you specify. However, the number of component devices in a RAID 10 array does not need to be a multiple of the number of replicas of each data block. The effective storage size is the number of devices divided by the number of replicas.
For example, if you specify two replicas for an array created with five component devices, a copy of each block is stored on two different devices. The effective storage size for one copy of all data is 5/2 or 2.5 times the size of a component device.
9.2.2 Layout #
The complex RAID 10 setup supports three different layouts which define how the data blocks are arranged on the disks. The available layouts are near (default), far and offset. They have different performance characteristics, so it is important to choose the right layout for your workload.
9.2.2.1 Near Layout #
With the near layout, copies of a block of data are striped near each other on different component devices. That is, multiple copies of one data block are at similar offsets in different devices. Near is the default layout for RAID 10. For example, if you use an odd number of component devices and two copies of data, some copies are perhaps one chunk further into the device.
The near layout for the complex RAID 10 yields read and write performance similar to RAID 0 over half the number of drives.
Near layout with an even number of disks and two replicas:
sda1 sdb1 sdc1 sde1 0 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9
Near layout with an odd number of disks and two replicas:
sda1 sdb1 sdc1 sde1 sdf1 0 0 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 9 9 10 10 11 11 12
9.2.2.2 Far Layout #
The far layout stripes data over the early part of all drives, then stripes a second copy of the data over the later part of all drives, making sure that all copies of a block are on different drives. The second set of values starts halfway through the component drives.
With a far layout, the read performance of the complex RAID 10 is similar to a RAID 0 over the full number of drives, but write performance is substantially slower than a RAID 0 because there is more seeking of the drive heads. It is best used for read-intensive operations such as for read-only file servers.
The speed of the RAID 10 for writing is similar to other mirrored RAID types, like RAID 1 and RAID 10 using near layout, as the elevator of the file system schedules the writes in a more optimal way than raw writing. Using RAID 10 in the far layout is well suited for mirrored writing applications.
Far layout with an even number of disks and two replicas:
sda1 sdb1 sdc1 sde1 0 1 2 3 4 5 6 7 . . . 3 0 1 2 7 4 5 6
Far layout with an odd number of disks and two replicas:
sda1 sdb1 sdc1 sde1 sdf1 0 1 2 3 4 5 6 7 8 9 . . . 4 0 1 2 3 9 5 6 7 8
9.2.2.3 Offset Layout #
The offset layout duplicates stripes so that the multiple copies of a given chunk are laid out on consecutive drives and at consecutive offsets. Effectively, each stripe is duplicated and the copies are offset by one device. This should give similar read characteristics to a far layout if a suitably large chunk size is used, but without as much seeking for writes.
Offset layout with an even number of disks and two replicas:
sda1 sdb1 sdc1 sde1 0 1 2 3 3 0 1 2 4 5 6 7 7 4 5 6 8 9 10 11 11 8 9 10
Offset layout with an odd number of disks and two replicas:
sda1 sdb1 sdc1 sde1 sdf1 0 1 2 3 4 4 0 1 2 3 5 6 7 8 9 9 5 6 7 8 10 11 12 13 14 14 10 11 12 13
9.2.2.4 Specifying the number of Replicas and the Layout with YaST and mdadm #
The number of replicas and the layout is specified as --layout
parameter for mdadm. The following values are accepted:
nN
Specify
n
for near layout and replace N with the number of replicas.n2
is the default that is used when not configuring layout and the number of replicas.fN
Specify
f
for far layout and replace N with the number of replicas.oN
Specify
o
for offset layout and replace N with the number of replicas.
YaST automatically offers a selection of all possible values for the
parameter.9.2.3 Creating a Complex RAID 10 with the YaST Partitioner #
Launch YaST and open the Partitioner.
If necessary, create partitions that should be used with your RAID configuration. Do not format them and set the partition type to Book “Deployment Guide”, Chapter 10 “Expert Partitioner”, Section 10.1 “Using the Expert Partitioner” for details.
. When using existing partitions it is not necessary to change their partition type—YaST will automatically do so. Refer toFor RAID 10 at least four partitions are needed. It is strongly recommended to use partitions stored on different hard disks to decrease the risk of losing data if one is defective. It is recommended to use only partitions of the same size because each segment can contribute only the same amount of space as the smallest sized partition.
In the left panel, select
.A list of existing RAID configurations opens in the right panel.
At the lower left of the RAID page, click
.Under
, select .You can optionally assign a
to your RAID. It will make it available as/dev/md/NAME
. See Section 7.2.1, “RAID Names” for more information.In the
list, select the desired partitions, then click to move them to the list.(Optional) Click
to specify the preferred order of the disks in the RAID array.For RAID types such as RAID 10, where the order of added disks matters, you can specify the order in which the devices will be used. This will ensure that one half of the array resides on one disk subsystem and the other half of the array resides on a different disk subsystem. For example, if one disk subsystem fails, the system keeps running from the second disk subsystem.
Select each disk in turn and click one of the
buttons, where X is the letter you want to assign to the disk. Available classes are A, B, C, D and E but for many cases fewer classes are needed (only A and B, for example). Assign all available RAID disks this way.You can press the Ctrl or Shift key to select multiple devices. You can also right-click a selected device and choose the appropriate class from the context menu.
Specify the order of the devices by selecting one of the sorting options:
Sorts all devices of class A before all devices of class B and so on. For example: :
AABBCC
.Sorts devices by the first device of class A, then first device of class B, then all the following classes with assigned devices. Then the second device of class A, the second device of class B, and so on follows. All devices without a class are sorted to the end of the devices list. For example: :
ABCABC
.Pattern File: Select an existing file that contains multiple lines, where each is a regular expression and a class name (
"sda.* A"
). All devices that match the regular expression are assigned to the specified class for that line. The regular expression is matched against the kernel name (/dev/sda1
), the udev path name (/dev/disk/by-path/pci-0000:00:1f.2-scsi-0:0:0:0-part1
) and then the udev ID (dev/disk/by-id/ata-ST3500418AS_9VMN8X8L-part1
). The first match made determines the class if a device’s name matches more than one regular expression.At the bottom of the dialog, click
to confirm the order.
Click
.Under
, specify the and , then click .For a RAID 10, the parity options are n (near), f (far), and o (offset). The number indicates the number of replicas of each data block that are required. Two is the default. For information, see Section 9.2.2, “Layout”.
Add a file system and mount options to the RAID device, then click
.Click
.Verify the changes to be made, then click
to create the RAID.
9.2.4 Creating a Complex RAID 10 with mdadm #
The procedure in this section uses the device names shown in the following table. Ensure that you modify the device names with the names of your own devices.
Raw Devices |
RAID 10 |
---|---|
|
|
Open a terminal.
If necessary, create at least four 0xFD Linux RAID partitions of equal size using a disk partitioner such as parted.
Create a RAID 10 by entering the following command.
>
sudo
mdadm --create /dev/md3 --run --level=10 --chunk=32 --raid-devices=4 \ /dev/sdf1 /dev/sdg1 /dev/sdh1 /dev/sdi1Make sure to adjust the value for
--raid-devices
and the list of partitions according to your setup.The command creates an array with near layout and two replicas. To change any of the two values, use the
--layout
as described in Section 9.2.2.4, “Specifying the number of Replicas and the Layout with YaST and mdadm”.Create a file system on the RAID 10 device
/dev/md3
, for example an XFS file system:>
sudo
mkfs.xfs /dev/md3Modify the command to use a different file system.
Edit the
/etc/mdadm.conf
file or create it, if it does not exist (for example by runningsudo vi /etc/mdadm.conf
). Add the following lines (if the file exists, the first line probably already exists, too).DEVICE containers partitions ARRAY /dev/md3 UUID=UUID
The UUID of the device can be retrieved with the following command:
>
sudo
mdadm -D /dev/md3 | grep UUIDEdit the
/etc/fstab
file to add an entry for the RAID 10 device/dev/md3
. The following example shows an entry for a RAID device with the XFS file system and/data
as a mount point./dev/md3 /data xfs defaults 1 2
Mount the RAID device:
>
sudo
mount /data
10 Creating a Degraded RAID Array #
A degraded array is one in which some devices are missing. Degraded arrays are supported only for RAID 1, RAID 4, RAID 5, and RAID 6. These RAID types are designed to withstand some missing devices as part of their fault-tolerance features. Typically, degraded arrays occur when a device fails. It is possible to create a degraded array on purpose.
RAID Type |
Allowable Number of Slots Missing | |
---|---|---|
RAID 1 |
All but one device | |
RAID 4 |
One slot | |
RAID 5 |
One slot | |
RAID 6 |
One or two slots |
To create a degraded array in which some devices are missing, simply give the
word missing
in place of a device name. This causes
mdadm
to leave the corresponding slot in the array empty.
When creating a RAID 5 array, mdadm
automatically creates
a degraded array with an extra spare drive. This is because building the
spare into a degraded array is generally faster than resynchronizing the
parity on a non-degraded, but not clean, array. You can override this feature
with the --force
option.
Creating a degraded array might be useful if you want create a RAID, but one of the devices you want to use already has data on it. In that case, you create a degraded array with other devices, copy data from the in-use device to the RAID that is running in degraded mode, add the device into the RAID, then wait while the RAID is rebuilt so that the data is now across all devices. An example of this process is given in the following procedure:
To create a degraded RAID 1 device
/dev/md0
, using one single drive/dev/sd1
, enter the following at the command prompt:>
sudo
mdadm --create /dev/md0 -l 1 -n 2 /dev/sda1 missingThe device should be the same size or larger than the device you plan to add to it.
If the device you want to add to the mirror contains data that you want to move to the RAID array, copy it now to the RAID array while it is running in degraded mode.
Add the device you copied the data from to the mirror. For example, to add
/dev/sdb1
to the RAID, enter the following at the command prompt:>
sudo
mdadm /dev/md0 -a /dev/sdb1You can add only one device at a time. You must wait for the kernel to build the mirror and bring it fully online before you add another mirror.
Monitor the build progress by entering the following at the command prompt:
>
sudo
cat /proc/mdstatTo see the rebuild progress while being refreshed every second, enter
>
sudo
watch -n 1 cat /proc/mdstat
11 Resizing Software RAID Arrays with mdadm #
This section describes how to increase or reduce the size of a software
RAID 1, 4, 5, or 6 device with the Multiple Device Administration
(mdadm(8)
) tool.
Resizing an existing software RAID device involves increasing or decreasing the space contributed by each component partition. The file system that resides on the RAID must also be able to be resized to take advantage of the changes in available space on the device. In SUSE Linux Enterprise Server, file system resizing utilities are available for file systems Btrfs, Ext2, Ext3, Ext4, and XFS (increase size only). Refer to Chapter 2, Resizing File Systems for more information.
The mdadm
tool supports resizing only for software RAID
levels 1, 4, 5, and 6. These RAID levels provide disk fault tolerance so that
one component partition can be removed at a time for resizing. In principle,
it is possible to perform a hot resize for RAID partitions, but you must take
extra care for your data when doing so.
Resizing any partition or file system involves some risks that can potentially result in losing data. To avoid data loss, ensure that you back up your data before you begin any resizing task.
Resizing the RAID involves the following tasks. The order in which these tasks are performed depends on whether you are increasing or decreasing its size.
Tasks |
Description |
Order If Increasing Size |
Order If Decreasing Size |
---|---|---|---|
Resize each of the component partitions. |
Increase or decrease the active size of each component partition. You remove only one component partition at a time, modify its size, then return it to the RAID. |
1 |
2 |
Resize the software RAID itself. |
The RAID does not automatically know about the increases or decreases you make to the underlying component partitions. You must inform it about the new size. |
2 |
3 |
Resize the file system. |
You must resize the file system that resides on the RAID. This is possible only for file systems that provide tools for resizing. |
3 |
1 |
The procedures in the following sections use the device names shown in the following table. Ensure that you modify the names to use the names of your own devices.
RAID Device |
Component Partitions |
---|---|
|
|
11.1 Increasing the Size of a Software RAID #
Increasing the size of a software RAID involves the following tasks in the given order: increase the size of all partitions the RAID consists of, increase the size of the RAID itself and, finally, increase the size of the file system.
If a RAID does not have disk fault tolerance, or it is simply not consistent, data loss results if you remove any of its partitions. Be very careful when removing partitions, and ensure that you have a backup of your data available.
11.1.1 Increasing the Size of Component Partitions #
Apply the procedure in this section to increase the size of a RAID 1, 4, 5, or 6. For each component partition in the RAID, remove the partition from the RAID, modify its size, return it to the RAID, then wait until the RAID stabilizes to continue. While a partition is removed, the RAID operates in degraded mode and has no or reduced disk fault tolerance. Even for RAIDs that can tolerate multiple concurrent disk failures, do not remove more than one component partition at a time. To increase the size of the component partitions for the RAID, proceed as follows:
Open a terminal.
Ensure that the RAID array is consistent and synchronized by entering
>
cat /proc/mdstatIf your RAID array is still synchronizing according to the output of this command, you must wait until synchronization is complete before continuing.
Remove one of the component partitions from the RAID array. For example, to remove
/dev/sda1
, enter>
sudo
mdadm /dev/md0 --fail /dev/sda1 --remove /dev/sda1To succeed, both the fail and remove actions must be specified.
Increase the size of the partition that you removed in the previous step by doing one of the following:
Increase the size of the partition, using a disk partitioner such as the YaST Partitioner or the command line tool parted. This option is the usual choice.
Replace the disk on which the partition resides with a higher-capacity device. This option is possible only if no other file systems on the original disk are accessed by the system. When the replacement device is added back into the RAID, it takes much longer to synchronize the data because all of the data that was on the original device must be rebuilt.
Re-add the partition to the RAID array. For example, to add
/dev/sda1
, enter>
sudo
mdadm -a /dev/md0 /dev/sda1Wait until the RAID is synchronized and consistent before continuing with the next partition.
Repeat these steps for each of the remaining component devices in the array. Ensure that you modify the commands for the correct component partition.
If you get a message that tells you that the kernel could not re-read the partition table for the RAID, you must reboot the computer after all partitions have been resized to force an update of the partition table.
Continue with Section 11.1.2, “Increasing the Size of the RAID Array”.
Alternatively, if you are replacing the disks and can install the new disks temporarily alongside the existing array, you can hot-replace the partitions. This will keep them in service until a new partition has been rebuilt as a spare, so the array does not enter a degraded state and remains fault-tolerant during the process. The following steps replace steps 3–5 in the above procedure.
Mark a component partition for replacement. For example, to replace
/dev/sda1
, enter>
sudo
mdadm /dev/md0 --replace /dev/sda1Add a replacement partition to the RAID array. For example, to add
/dev/sdd1
, enter>
sudo
mdadm -a /dev/md0 /dev/sdd1Once the new partition has been added and has finished rebuilding, the partition marked for replacement will be automatically marked as faulty, and can be removed from the array. For example, to remove
/dev/sda1
, enter>
sudo
mdadm /dev/md0 --remove /dev/sda1
11.1.2 Increasing the Size of the RAID Array #
After you have resized each of the component partitions in the RAID (see Section 11.1.1, “Increasing the Size of Component Partitions”), the RAID array configuration continues to use the original array size until you force it to be aware of the newly available space. You can specify a size for the RAID or use the maximum available space.
The procedure in this section uses the device name
/dev/md0
for the RAID device. Ensure that you modify
the name to use the name of your own device.
Open a terminal.
Ensure that the RAID array is consistent and synchronized by entering
>
cat /proc/mdstatIf your RAID array is still synchronizing according to the output of this command, you must wait until synchronization is complete before continuing.
Check the size of the array and the device size known to the array by entering
>
sudo
mdadm -D /dev/md0 | grep -e "Array Size" -e "Dev Size"Do one of the following:
Increase the size of the array to the maximum available size by entering
>
sudo
mdadm --grow /dev/md0 -z maxIncrease the size of the array to the maximum available size by entering
>
sudo
mdadm --grow /dev/md0 -z max --assume-cleanThe array uses any space that has been added to the devices, but this space will not be synchronized. This is recommended for RAID 1 because the synchronization is not needed. It can be useful for other RAID levels if the space that was added to the member devices was pre-zeroed.
Increase the size of the array to a specified value by entering
>
sudo
mdadm --grow /dev/md0 -z SIZEReplace SIZE with an integer value in kilobytes (a kilobyte is 1024 bytes) for the desired size.
Recheck the size of your array and the device size known to the array by entering
>
sudo
mdadm -D /dev/md0 | grep -e "Array Size" -e "Dev Size"Do one of the following:
If your array was successfully resized, continue with Section 11.1.3, “Increasing the Size of the File System”.
If your array was not resized as you expected, you must reboot, then try this procedure again.
11.1.3 Increasing the Size of the File System #
After you increase the size of the array (see Section 11.1.2, “Increasing the Size of the RAID Array”), you are ready to resize the file system.
You can increase the size of the file system to the maximum space available or specify an exact size. When specifying an exact size for the file system, ensure that the new size satisfies the following conditions:
The new size must be greater than the size of the existing data; otherwise, data loss occurs.
The new size must be equal to or less than the current RAID size because the file system size cannot extend beyond the space available.
Refer to Chapter 2, Resizing File Systems for detailed instructions.
11.2 Decreasing the Size of a Software RAID #
Decreasing the Size of a Software RAID involves the following tasks in the given order: decrease the size of the file system, decrease the size of all partitions the RAID consists of, and finally decrease the size of the RAID itself.
If a RAID does not have disk fault tolerance, or it is simply not consistent, data loss results if you remove any of its partitions. Be very careful when removing partitions, and ensure that you have a backup of your data available.
Decreasing the size of a file system formatted with XFS is not possible, since such a feature is not supported by XFS. As a consequence, the size of a RAID that uses the XFS file system cannot be decreased.
11.2.1 Decreasing the Size of the File System #
When decreasing the size of the file system on a RAID device, ensure that the new size satisfies the following conditions:
The new size must be greater than the size of the existing data; otherwise, data loss occurs.
The new size must be equal to or less than the current RAID size because the file system size cannot extend beyond the space available.
Refer to Chapter 2, Resizing File Systems for detailed instructions.
11.2.2 Decreasing the Size of the RAID Array #
After you have resized the file system (see
Section 11.2.1, “Decreasing the Size of the File System”), the
RAID array configuration continues to use the original array size until you
force it to reduce the available space. Use the mdadm
--grow
mode to force the RAID to use a smaller segment size. To
do this, you must use the -z option to specify the amount of space in
kilobytes to use from each device in the RAID. This size must be a multiple
of the chunk size, and it must leave about 128 KB of space for the RAID
superblock to be written to the device.
The procedure in this section uses the device name
/dev/md0
for the RAID device. Ensure that you modify
commands to use the name of your own device.
Open a terminal.
Check the size of the array and the device size known to the array by entering
>
sudo
mdadm -D /dev/md0 | grep -e "Array Size" -e "Dev Size"Decrease the array’s device size to a specified value by entering
>
sudo
mdadm --grow /dev/md0 -z SIZEReplace SIZE with an integer value in kilobytes for the desired size. (A kilobyte is 1024 bytes.)
For example, the following command sets the segment size for each RAID device to about 40 GB where the chunk size is 64 KB. It includes 128 KB for the RAID superblock.
>
sudo
mdadm --grow /dev/md2 -z 41943168Recheck the size of your array and the device size known to the array by entering
>
sudo
mdadm -D /dev/md0 | grep -e "Array Size" -e "Device Size"Do one of the following:
If your array was successfully resized, continue with Section 11.2.3, “Decreasing the Size of Component Partitions”.
If your array was not resized as you expected, you must reboot, then try this procedure again.
11.2.3 Decreasing the Size of Component Partitions #
After you decrease the segment size that is used on each device in the RAID (see Section 11.2.2, “Decreasing the Size of the RAID Array”), the remaining space in each component partition is not used by the RAID. You can leave partitions at their current size to allow for the RAID to grow at a future time, or you can reclaim this now unused space.
To reclaim the space, you decrease the component partitions one at a time. For each component partition, you remove it from the RAID, reduce its partition size, return the partition to the RAID, then wait until the RAID stabilizes. To allow for metadata, you should specify a slightly larger size than the size you specified for the RAID in Section 11.2.2, “Decreasing the Size of the RAID Array”.
While a partition is removed, the RAID operates in degraded mode and has no or reduced disk fault tolerance. Even for RAIDs that can tolerate multiple concurrent disk failures, you should never remove more than one component partition at a time. To decrease the size of the component partitions for the RAID, proceed as follows:
Open a terminal.
Ensure that the RAID array is consistent and synchronized by entering
>
cat /proc/mdstatIf your RAID array is still synchronizing according to the output of this command, you must wait until synchronization is complete before continuing.
Remove one of the component partitions from the RAID array. For example, to remove
/dev/sda1
, enter>
sudo
mdadm /dev/md0 --fail /dev/sda1 --remove /dev/sda1To succeed, both the fail and remove actions must be specified.
Decrease the size of the partition that you removed in the previous step to a size that is slightly larger than the size you set for the segment size. The size should be a multiple of the chunk size and allow 128 KB for the RAID superblock. Use a disk partitioner such as the YaST partitioner or the command line tool parted to decrease the size of the partition.
Re-add the partition to the RAID array. For example, to add
/dev/sda1
, enter>
sudo
mdadm -a /dev/md0 /dev/sda1Wait until the RAID is synchronized and consistent before continuing with the next partition.
Repeat these steps for each of the remaining component devices in the array. Ensure that you modify the commands for the correct component partition.
If you get a message that tells you that the kernel could not re-read the partition table for the RAID, you must reboot the computer after resizing all of its component partitions.
(Optional) Expand the size of the RAID and file system to use the maximum amount of space in the now smaller component partitions and increase the size of the file system afterward. Refer to Section 11.1.2, “Increasing the Size of the RAID Array” for instructions.
12 Storage Enclosure LED Utilities for MD Software RAIDs #
Storage enclosure LED Monitoring utility (ledmon
) and
LED Control (ledctl
) utility are Linux user space
applications that use a broad range of interfaces and protocols to control
storage enclosure LEDs. The primary usage is to visualize the status of
Linux MD software RAID devices created with the mdadm utility. The
ledmon
daemon monitors the status
of the drive array and updates the status of the drive LEDs. The
ledctl
utility allows you to set LED patterns for
specified devices.
These LED utilities use the SGPIO (Serial General Purpose Input/Output) specification (Small Form Factor (SFF) 8485) and the SCSI Enclosure Services (SES) 2 protocol to control LEDs. They implement the International Blinking Pattern Interpretation (IBPI) patterns of the SFF-8489 specification for SGPIO. The IBPI defines how the SGPIO standards are interpreted as states for drives and slots on a backplane and how the backplane should visualize the states with LEDs.
Some storage enclosures do not adhere strictly to the SFF-8489 specification. An enclosure processor might accept an IBPI pattern but not blink the LEDs according to the SFF-8489 specification, or the processor might support only a limited number of the IBPI patterns.
LED management (AHCI) and SAF-TE protocols are not supported by the
ledmon
and ledctl
utilities.
The ledmon
and
ledctl
applications have been verified to work with Intel
storage controllers such as the Intel AHCI controller and Intel SAS
controller. They also support PCIe-SSD (solid-state drive) enclosure LEDs to
control the storage enclosure status (OK, Fail, Rebuilding) LEDs of PCIe-SSD
devices that are part of an MD software RAID volume. The applications might
also work with the IBPI-compliant storage controllers of other vendors
(especially SAS/SCSI controllers); however, other vendors’ controllers have
not been tested.
ledmon
and ledctl
are part of the ledmon
package,
which is not installed by default. Run sudo zypper in
ledmon
to install it.
12.1 The Storage Enclosure LED Monitor Service #
The ledmon
application is a daemon
process that constantly monitors the state of MD software RAID devices or
the state of block devices in a storage enclosure or drive bay. Only a
single instance of the daemon should be running at a time. The
ledmon
daemon is part of Intel
Enclosure LED Utilities.
The state is visualized on LEDs associated with each slot in a storage array enclosure or a drive bay. The application monitors all software RAID devices and visualizes their state. It does not provide a way to monitor only selected software RAID volumes.
The ledmon
daemon supports two types
of LED systems: A two-LED system (Activity LED and Status LED) and a
three-LED system (Activity LED, Locate LED, and Fail LED). This tool has the
highest priority when accessing the LEDs.
To start ledmon
, enter
>
sudo
ledmon [options]
where [options] is one or more of the following:
ledmon
#-c PATH
,--confg=PATH
The configuration is read from
~/.ledctl
or from/etc/ledcfg.conf
if existing. Use this option to specify an alternative configuration file.Currently this option has no effect, since support for configuration files has not been implemented yet. See
man 5 ledctl.conf
for details.- -l PATH , --log=PATH
Sets a path to local log file. If this user-defined file is specified, the global log file
/var/log/ledmon.log
is not used.-t SECONDS
,--interval=SECONDS
Sets the time interval between scans of
sysfs
. The value is given in seconds. The minimum is 5 seconds. The maximum is not specified.--quiet
,--error
,--warning
,--info
,--debug
,--all
Specifies the verbosity level. The level options are specified in the order of no information to the most information. Use the
--quiet
option for no logging. Use the--all
option to log everything. If you specify more than one verbose option, the last option in the command applies.-h
,--help
Prints the command information to the console, then exits.
-v
,--version
Displays version of
ledmon
and information about the license, then exits.
The ledmon
daemon does not recognize the PFA (Predicted
Failure Analysis) state from the SFF-8489 specification. Thus, the PFA
pattern is not visualized.
12.2 The Storage Enclosure LED Control Application #
The Enclosure LED Application (ledctl
) is a user space
application that controls LEDs associated with each slot in a storage
enclosure or a drive bay. The ledctl
application is a
part of Intel Enclosure LED Utilities.
When you issue the command, the LEDs of the specified devices are set to a
specified pattern and all other LEDs are turned off. This application needs
to be run with root
privileges. Because the
ledmon
application has the
highest priority when accessing LEDs, some patterns set by
ledctl
might have no effect if the
ledmon
daemon is running (except for
the Locate pattern).
The ledctl
application supports two types of LED systems:
A two-LED system (Activity LED and Status LED) and a three-LED system
(Activity LED, Fail LED, and Locate LED).
To start ledctl
, enter
>
sudo
[options] PATTERN_NAME=list_of_devices
where [options] is one or more of the following:
-c PATH
,--confg=PATH
Sets a path to local configuration file. If this option is specified, the global configuration file and user configuration file have no effect.
- -l PATH , --log=PATH
Sets a path to local log file. If this user-defined file is specified, the global log file
/var/log/ledmon.log
is not used.--quiet
Turns off all messages sent to
stdout
orstderr
out. The messages are still logged to local file and thesyslog
facility.-h
,--help
Prints the command information to the console, then exits.
-v
,--version
Displays version of
ledctl
and information about the license, then exits.
12.2.1 Pattern Names #
The ledctl
application accepts the following names for
argument, according to the SFF-8489
specification.
locate
Turns on the Locate LED associated with the specified devices or empty slots. This state is used to identify a slot or drive.
locate_off
Turns off the Locate LED associated with the specified devices or empty slots.
normal
Turns off the Status LED, Failure LED, and Locate LED associated with the specified devices.
off
Turns off only the Status LED and Failure LED associated with the specified devices.
ica
,degraded
Visualizes the
In a Critical Array
pattern.rebuild
,rebuild_p
Visualizes the
Rebuild
pattern. This supports both of the rebuild states for compatibility and legacy reasons.ifa
,failed_array
Visualizes the
In a Failed Array
pattern.hotspare
Visualizes the
Hotspare
pattern.pfa
Visualizes the
Predicted Failure Analysis
pattern.failure
,disk_failed
Visualizes the
Failure
pattern.- ses_abort
SES-2 R/R ABORT
ses_rebuild
SES-2 REBUILD/REMAP
ses_ifa
SES-2 IN FAILED ARRAY
ses_ica
SES-2 IN CRITICAL ARRAY
ses_cons_check
SES-2 CONS CHECK
ses_hotspare
SES-2 HOTSPARE
ses_rsvd_dev
SES-2 RSVD DEVICE
ses_ok
SES-2 OK
ses_ident
SES-2 IDENT
ses_rm
SES-2 REMOVE
ses_insert
SES-2 INSERT
ses_missing
SES-2 MISSING
ses_dnr
SES-2 DO NOT REMOVE
ses_active
SES-2 ACTIVE
ses_enable_bb
SES-2 ENABLE BYP B
ses_enable_ba
SES-2 ENABLE BYP A
ses_devoff
SES-2 DEVICE OFF
ses_fault
SES-2 FAULT
When a non-SES-2 pattern is sent to a device in an enclosure, the pattern is automatically translated to the SCSI Enclosure Services (SES) 2 pattern as shown above.
Non-SES-2 Pattern |
SES-2 Pattern |
---|---|
locate |
ses_ident |
locate_off |
ses_ident |
normal |
ses_ok |
off |
ses_ok |
ica |
ses_ica |
degraded |
ses_ica |
rebuild |
ses_rebuild |
rebuild_p |
ses_rebuild |
ifa |
ses_ifa |
failed_array |
ses_ifa |
hotspare |
ses_hotspare |
pfa |
ses_rsvd_dev |
failure |
ses_fault |
disk_failed |
ses_fault |
12.2.2 List of Devices #
When you issue the ledctl
command, the LEDs of the
specified devices are set to the specified pattern and all other LEDs are
turned off. The list of devices can be provided in one of two formats:
A list of devices separated by a comma and no spaces
A list in curly braces with devices separated by a space
If you specify multiple patterns in the same command, the device list for each pattern can use the same or different format. For examples that show the two list formats, see Section 12.2.3, “Examples”.
A device is a path to file in the /dev
directory or in
the /sys/block
directory. The path can identify a
block device, an MD software RAID device, or a container device. For a
software RAID device or a container device, the reported LED state is set
for all of the associated block devices.
The LEDs of devices listed in list_of_devices are set to the given pattern pattern_name and all other LEDs are turned off.
12.2.3 Examples #
To locate a single block device:
>
sudo
ledctl locate=/dev/sda
To turn off the Locate LED for a single block device:
>
sudo
ledctl locate_off=/dev/sda
To locate disks of an MD software RAID device and to set a rebuild pattern for two of its block devices at the same time:
>
sudo
ledctl locate=/dev/md127 rebuild={ /sys/block/sd[a-b] }
To turn off the Status LED and Failure LED for the specified devices:
>
sudo
ledctl off={ /dev/sda /dev/sdb }
To locate three block devices, run one of the following commands (both are equivalent):
>
sudo
ledctl locate=/dev/sda,/dev/sdb,/dev/sdc>
sudo
ledctl locate={ /dev/sda /dev/sdb /dev/sdc }
12.3 Additional Information #
See the following resources for details about the LED patterns and monitoring tools:
13 Toubleshooting software RAIDs #
Check the /proc/mdstat
file to find out whether a RAID
partition has been damaged. If a disk fails,
replace the defective hard disk with a new one partitioned the same way.
Then restart your system and enter the command mdadm /dev/mdX --add
/dev/sdX
. Replace X
with your particular device
identifiers. This integrates the hard disk automatically into the RAID
system and fully reconstructs it (for all RAID levels except for
RAID 0).
Although you can access all data during the rebuild, you might encounter some performance issues until the RAID has been fully rebuilt.
13.1 Recovery after Failing Disk is Back Again #
There are several reasons a disk included in a RAID array may fail. Here is a list of the most common ones:
Problems with the disk media.
Disk drive controller failure.
Broken connection to the disk.
In the case of the disk media or controller failure, the device needs to be replaced or repaired. If a hot-spare was not configured within the RAID, then manual intervention is required.
In the last case, the failed device can be automatically re-added by the
mdadm
command after the connection is repaired (which
might be automatic).
Because md
/mdadm
cannot reliably
determine what caused the disk failure, it assumes a serious disk error and
treats any failed device as faulty until it is explicitly told that the
device is reliable.
Under some circumstances—such as storage devices with the internal
RAID array— the connection problems are very often the cause of the
device failure. In such case, you can tell mdadm
that it
is safe to automatically --re-add
the device after it
appears. You can do this by adding the following line to
/etc/mdadm.conf
:
POLICY action=re-add
Note that the device will be automatically re-added after re-appearing only
if the udev
rules cause mdadm -I
DISK_DEVICE_NAME
to be run on any
device that spontaneously appears (default behavior), and if write-intent
bitmaps are configured (they are by default).
If you want this policy to only apply to some devices and not to the
others, then the path=
option can be added to the
POLICY
line in /etc/mdadm.conf
to
restrict the non-default action to only selected devices. Wild cards can be
used to identify groups of devices. See man 5 mdadm.conf
for more information.
Part IV Network Storage #
- 14 iSNS for Linux
Storage area networks (SANs) can contain many disk drives that are dispersed across complex networks. This can make device discovery and device ownership difficult. iSCSI initiators must be able to identify storage resources in the SAN and determine whether they have access to them.
- 15 Mass Storage over IP Networks: iSCSI
One of the primary tasks of a computer center, or any site that supports servers, is to provide adequate disk capacity. Fibre Channel is often used for this purpose. iSCSI (Internet SCSI) solutions provide a lower-cost alternative to Fibre Channel that can leverage commodity servers and Ethernet net…
- 16 Fibre Channel Storage over Ethernet Networks: FCoE
Many enterprise data centers rely on Ethernet for their LAN and data traffic, and on Fibre Channel networks for their storage infrastructure. Open Fibre Channel over Ethernet (FCoE) Initiator software allows servers with Ethernet adapters to connect to a Fibre Channel storage subsystem over an Ether…
- 17 NVMe-oF
This chapter describes how to set up an NVMe-oF host and target.
- 18 Managing Multipath I/O for Devices
This section describes how to manage failover and path load balancing for multiple paths between the servers and block storage devices by using Multipath I/O (MPIO).
- 19 Managing Access Control Lists over NFSv4
There is no single standard for Access Control Lists (ACLs) in Linux beyond the simple read, write, and execute (rwx) flags for user, group, and others (ugo). One option for finer control is the Draft POSIX ACLs, which were never formally standardized by POSIX. Another is the NFSv4 ACLs, which were …
14 iSNS for Linux #
Storage area networks (SANs) can contain many disk drives that are dispersed across complex networks. This can make device discovery and device ownership difficult. iSCSI initiators must be able to identify storage resources in the SAN and determine whether they have access to them.
Internet Storage Name Service (iSNS) is a standards-based service that simplifies the automated discovery, management, and configuration of iSCSI devices on a TCP/IP network. iSNS provides intelligent storage discovery and management services comparable to those found in Fibre Channel networks.
Without iSNS, you must know the host name or IP address of each node where targets of interest are located. In addition, you must manually manage which initiators can access which targets yourself using mechanisms such as access control lists.
iSNS should only be used in secure internal networking environments, as the network traffic is not encrypted.
14.1 How iSNS Works #
For an iSCSI initiator to discover iSCSI targets, it needs to identify which devices in the network are storage resources and what IP addresses it needs to access them. A query to an iSNS server returns a list of iSCSI targets and the IP addresses that the initiator has permission to access.
Using iSNS, you create iSNS discovery domains into which you then group or organize iSCSI targets and initiators. By dividing storage nodes into domains, you can limit the discovery process of each host to the most appropriate subset of targets registered with iSNS, which allows the storage network to scale by reducing the number of unnecessary discoveries and by limiting the amount of time each host spends establishing discovery relationships. This lets you control and simplify the number of targets and initiators that must be discovered.
Both iSCSI targets and iSCSI initiators can use iSNS clients to initiate transactions with iSNS servers by using the iSNS protocol. They then register device attribute information in a common discovery domain, download information about other registered clients, and receive asynchronous notification of events that occur in their discovery domain.
iSNS servers respond to iSNS protocol queries and requests made by iSNS clients using the iSNS protocol. iSNS servers initiate iSNS protocol state change notifications and store properly authenticated information submitted by a registration request in an iSNS database.
Benefits provided by iSNS for Linux include:
Provides an information facility for registration, discovery, and management of networked storage assets.
Integrates with the DNS infrastructure.
Consolidates registration, discovery, and management of iSCSI storage.
Simplifies storage management implementations.
Improves scalability compared to other discovery methods.
iSNS offers several important benefits.
For example, in a setup with 100 iSCSI initiators and 100 iSCSI targets, all iSCSI initiators could potentially try to discover and connect to any of the 100 iSCSI targets. By grouping initiators and targets into discovery domains, you can prevent iSCSI initiators in one department from discovering the iSCSI targets in another department.
Another advantage of using iSNS is that the iSCSI clients only need to know the hostname or IP address of the iSNS server, rather than having to know the hostnames or IP addresses of a hundred servers.
14.2 Installing iSNS Server for Linux #
iSNS Server for Linux is included with SUSE Linux Enterprise Server, but is not installed
or configured by default. You need to install the package
open-isns
and configure the iSNS
service.
iSNS can be installed on the same server where iSCSI target or iSCSI initiator software is installed. Installing both the iSCSI target software and iSCSI initiator software on the same server is not supported.
To install iSNS for Linux:
Start YaST and select
› .In case
open-isns
is not installed yet, you are prompted to install it now. Confirm by clicking .The iSNS Service configuration dialog opens automatically to the
tab.In
, select one of the following:When Booting: The iSNS service starts automatically on server start-up.
Manually (Default): The iSNS service must be started manually by entering
sudo systemctl start isnsd
at the server console of the server where you install it.
Specify the following firewall settings:
Open Port in Firewall: Select the check box to open the firewall and allow access to the service from remote computers. The firewall port is closed by default.
Firewall Details: If you open the firewall port, the port is open on all network interfaces by default. Click to select interfaces on which to open the port, select the network interfaces to use, then click .
Click
to apply the configuration settings and complete the installation.Continue with Section 14.3, “Configuring iSNS Discovery Domains”.
14.3 Configuring iSNS Discovery Domains #
For iSCSI initiators and targets to use the iSNS service, they must belong to a discovery domain.
The iSNS service must be installed and running to configure iSNS discovery domains. For information, see Section 14.4, “Starting the iSNS Service”.
14.3.1 Creating iSNS Discovery Domains #
A default discovery domain named
is automatically created when you install the iSNS service. The existing iSCSI targets and initiators that have been configured to use iSNS are automatically added to the default discovery domain.To create a new discovery domain:
Start YaST and under
, select .Click the
tab.The
area lists all existing discovery domains. You can , or existing ones. Keep in mind that deleting an iSCSI node from domain membership removes it from the domain, but it does not delete the iSCSI node.The
area lists all iSCSI nodes assigned to a selected discovery domain. Selecting a different discovery domain refreshes the list with members from that discovery domain. You can add and delete iSCSI nodes from a selected discovery domain. Deleting an iSCSI node removes it from the domain, but it does not delete the iSCSI node.When an iSCSI initiator performs a discovery request, the iSNS service returns all iSCSI node targets that are members of the same discovery domain.
Click the
button.You can also select an existing discovery domain and click the
button to remove that discovery domain.Specify the name of the discovery domain you are creating, then click
.Continue with Section 14.3.2, “Adding iSCSI Nodes to a Discovery Domain”.
14.3.2 Adding iSCSI Nodes to a Discovery Domain #
Start YaST and under
, select .Click the
tab.Review the list of nodes to ensure that the iSCSI targets and initiators that you want to use the iSNS service are listed.
If an iSCSI target or initiator is not listed, you might need to restart the iSCSI service on the node. You can do this by running
>
sudo
systemctl restart iscsid.socket>
sudo
systemctl restart iscsito restart an initiator or
>
sudo
systemctl restart target-isnsto restart a target.
You can select an iSCSI node and click the
button to remove that node from the iSNS database. This is useful if you are no longer using an iSCSI node or have renamed it.The iSCSI node is automatically added to the list (iSNS database) again when you restart the iSCSI service or reboot the server unless you remove or comment out the iSNS portion of the iSCSI configuration file.
Click the
tab and select the desired discovery domain.Click
, select the node you want to add to the domain, then click .Repeat the previous step for as many nodes as you want to add to the discovery domain, then click
when you are finished adding nodes.Note that an iSCSI node can belong to more than one discovery domain.
14.4 Starting the iSNS Service #
iSNS must be started at the server where you install it. If you have not configured it to be started at boot time (see Section 14.2, “Installing iSNS Server for Linux” for details), enter the following command at a terminal:
>
sudo
systemctl start isnsd
You can also use the stop
, status
, and
restart
options with iSNS.
14.5 Further Information #
The following projects provide further information on iSNS and iSCSI:
General information about iSNS is available in RFC 4171: Internet Storage Name Service at https://datatracker.ietf.org/doc/html/rfc4171.
15 Mass Storage over IP Networks: iSCSI #
One of the primary tasks of a computer center, or any site that supports servers, is to provide adequate disk capacity. Fibre Channel is often used for this purpose. iSCSI (Internet SCSI) solutions provide a lower-cost alternative to Fibre Channel that can leverage commodity servers and Ethernet networking equipment. Linux iSCSI provides iSCSI initiator and iSCSI LIO target software for connecting Linux servers to central storage systems.
LIO is the standard open source multiprotocol SCSI target for Linux. LIO replaced the STGT (SCSI Target) framework as the standard unified storage target in Linux with Linux kernel version 2.6.38 and later. In SUSE Linux Enterprise Server 12 the iSCSI LIO Target Server replaces the iSCSI Target Server from previous versions.
iSCSI is a storage networking protocol that simplifies data transfers of SCSI packets over TCP/IP networks between block storage devices and servers. iSCSI target software runs on the target server and defines the logical units as iSCSI target devices. iSCSI initiator software runs on different servers and connects to the target devices to make the storage devices available on that server.
The iSCSI LIO target server and iSCSI initiator servers communicate by sending SCSI packets at the IP level in your LAN. When an application running on the initiator server starts an inquiry for an iSCSI LIO target device, the operating system produces the necessary SCSI commands. The SCSI commands are then embedded in IP packets and encrypted as necessary by software that is commonly known as the iSCSI initiator. The packets are transferred across the internal IP network to the corresponding iSCSI remote station, called the iSCSI LIO target server, or simply the iSCSI target.
Many storage solutions provide access over iSCSI, but it is also possible to run a Linux server that provides an iSCSI target. In this case, it is important to set up a Linux server that is optimized for file system services. For more information about RAID, also see Chapter 7, Software RAID Configuration.
15.1 Installing the iSCSI LIO Target Server and iSCSI Initiator #
While the iSCSI initiator is installed by default (packages
open-iscsi
and
yast2-iscsi-client
), the iSCSI LIO
target packages need to be installed manually.
While it is possible to run initiator and target in the same system, this setup is not recommended.
To install the iSCSI LIO Target Server, run the following command in a terminal:
>
sudo
zypper in yast2-iscsi-lio-server
In case you need to install the iSCSI initiator or any of its dependencies,
run the command sudo zypper in yast2-iscsi-client
.
Alternatively, use the YaST Software Management module for installation.
Any packages required in addition to the ones mentioned above will either be automatically pulled in by the installer, or be installed when you first run the respective YaST module.
15.2 Setting Up an iSCSI LIO Target Server #
This section describes how to use YaST to configure an iSCSI LIO Target Server and set up iSCSI LIO target devices. You can use any iSCSI initiator software to access the target devices.
15.2.1 iSCSI LIO Target Service Start-up and Firewall Settings #
The iSCSI LIO Target service is by default configured to be started manually. You can configure the service to start automatically at boot time. If you use a firewall on the server and you want the iSCSI LIO targets to be available to other computers, you must open a port in the firewall for each adapter that you want to use for target access. TCP port 3260 is the port number for the iSCSI protocol, as defined by IANA (Internet Assigned Numbers Authority).
Start YaST and launch
› .Switch to the
tab.Under
, specify how you want the iSCSI LIO target service to be started:When Booting: The service starts automatically on server restart.
Manually: (Default) You must start the service manually after a server restart by running
sudo systemctl start targetcli
. The target devices are not available until you start the service.
If you use a firewall on the server and you want the iSCSI LIO targets to be available to other computers, open port 3260 in the firewall for each adapter interface that you want to use for target access. If the port is closed for all of the network interfaces, the iSCSI LIO targets are not available to other computers.
If you do not use a firewall on the server, the firewall settings are disabled. In this case skip the following steps and leave the configuration dialog with
or switch to another tab to continue with the configuration.On the
tab, select the check box to enable the firewall settings.Click not be opened. Save your settings with .
to view or configure the network interfaces to use. All available network interfaces are listed, and all are selected by default. Deselect all interfaces on which the port should
Click
to save and apply the iSCSI LIO Target service settings.
15.2.2 Configuring Authentication for Discovery of iSCSI LIO Targets and Initiators #
The iSCSI LIO Target Server software supports the PPP-CHAP (Point-to-Point Protocol Challenge Handshake Authentication Protocol), a three-way authentication method defined in the Internet Engineering Task Force (IETF) RFC 1994 (https://datatracker.ietf.org/doc/html/rfc1994). The server uses this authentication method for the discovery of iSCSI LIO targets and initiators, not for accessing files on the targets. If you do not want to restrict the access to the discovery, use . The option is enabled by default. Without requiring authentication all iSCSI LIO targets on this server can be discovered by any iSCSI initiator on the same network.
If authentication is needed for a more secure configuration, you can use incoming authentication, outgoing authentication, or both.
requires an iSCSI initiator to prove that it has the permissions to run a discovery on the iSCSI LIO target. The initiator must provide the incoming user name and password. requires the iSCSI LIO target to prove to the initiator that it is the expected target. The iSCSI LIO target must provide the outgoing user name and password to the iSCSI initiator. The password needs to be different for incoming and outgoing discovery. If authentication for discovery is enabled, its settings apply to all iSCSI LIO target groups.We recommend that you use authentication for target and initiator discovery in production environments for security reasons.
To configure authentication preferences for iSCSI LIO targets:
Start YaST and launch
› .Switch to the
tab.By default, authentication is disabled (
). To enable Authentication, select , or both.Provide credentials for the selected authentication method(s). The user name and password pair must be different for incoming and outgoing discovery.
Click
to save and apply the settings.
15.2.3 Preparing the Storage Space #
Before you configure LUNs for your iSCSI Target servers, you must prepare the storage you want to use. You can use the entire unformatted block device as a single LUN, or you can subdivide a device into unformatted partitions and use each partition as a separate LUN. The iSCSI target configuration exports the LUNs to iSCSI initiators.
You can use the Partitioner in YaST or the command line to set up the partitions. Refer to Book “Deployment Guide”, Chapter 10 “Expert Partitioner”, Section 10.1 “Using the Expert Partitioner” for details. iSCSI LIO targets can use unformatted partitions with Linux, Linux LVM, or Linux RAID file system IDs.
After you set up a device or partition for use as an iSCSI target, you never access it directly via its local path. Do not mount the partitions on the target server.
15.2.3.1 Partitioning Devices in a Virtual Environment #
You can use a virtual machine guest server as an iSCSI LIO Target Server. This section describes how to assign partitions to a Xen virtual machine. You can also use other virtual environments that are supported by SUSE Linux Enterprise Server.
In a Xen virtual environment, you must assign the storage space you want to use for the iSCSI LIO target devices to the guest virtual machine, then access the space as virtual disks within the guest environment. Each virtual disk can be a physical block device, such as an entire disk, partition, or volume, or it can be a file-backed disk image where the virtual disk is a single image file on a larger physical disk on the Xen host server. For the best performance, create each virtual disk from a physical disk or a partition. After you set up the virtual disks for the guest virtual machine, start the guest server, then configure the new blank virtual disks as iSCSI target devices by following the same process as for a physical server.
File-backed disk images are created on the Xen host server, then
assigned to the Xen guest server. By default, Xen stores file-backed
disk images in the
/var/lib/xen/images/VM_NAME
directory, where VM_NAME
is the name of the virtual machine.
15.2.4 Setting Up an iSCSI LIO Target Group #
You can use YaST to configure iSCSI LIO target devices. YaST uses the targetcli
software. iSCSI LIO targets
can use partitions with Linux, Linux LVM, or Linux RAID file system IDs.
Before you begin, choose the partitions you wish to use for back-end storage. The partitions do not have to be formatted—the iSCSI client can format them when connected, overwriting all existing formatting.
Start YaST and launch
› .Switch to the
tab.Click
, then define a new iSCSI LIO target group and devices:The iSCSI LIO Target software automatically completes the
, , , , and fields. is selected by default.If you have multiple network interfaces, use the IP address drop-down box to select the IP address of the network interface to use for this target group. To make the server accessible under all addresses, choose
.Deselect
if you do not want to require initiator authentication for this target group (not recommended).Click
. Enter the path of the device or partition or to add it. Optionally specify a name, then click . The LUN number is automatically generated, beginning with 0. A name is automatically generated if you leave the field empty.(Optional) Repeat the previous steps to add targets to this target group.
After all desired targets have been added to the group, click
.
On the
page, configure information for the initiators that are permitted to access LUNs in the target group:After you specify at least one initiator for the target group, the
, , , and buttons are enabled. You can use or to add initiators for the target group:Modify iSCSI Target: Options #Add: Add a new initiator entry for the selected iSCSI LIO target group.
Edit LUN: Configure which LUNs in the iSCSI LIO target group to map to a selected initiator. You can map each of the allocated targets to a preferred initiator.
Edit Auth: Configure the preferred authentication method for a selected initiator. You can specify no authentication, or you can configure incoming authentication, outgoing authentication, or both.
Delete: Remove a selected initiator entry from the list of initiators allocated to the target group.
Copy: Add a new initiator entry with the same LUN mappings and authentication settings as a selected initiator entry. This allows you to easily allocate the same shared LUNs, in turn, to each node in a cluster.
Click
, specify the initiator name, select or deselect the check box, then click to save the settings.Select an initiator entry, click
, modify the LUN mappings to specify which LUNs in the iSCSI LIO target group to allocate to the selected initiator, then click to save the changes.If the iSCSI LIO target group consists of multiple LUNs, you can allocate one or multiple LUNs to the selected initiator. By default, each of the available LUNs in the group are assigned to an initiator LUN.
To modify the LUN allocation, perform one or more of the following actions:
Add: Click to create a new entry, then use the drop-down box to map a target LUN to it.
Delete: Select the entry, then click to remove a target LUN mapping.
Change: Select the entry, then use the drop-down box to select which Target LUN to map to it.
Typical allocation plans include the following:
A single server is listed as an initiator. All of the LUNs in the target group are allocated to it.
You can use this grouping strategy to logically group the iSCSI SAN storage for a given server.
Multiple independent servers are listed as initiators. One or multiple target LUNs are allocated to each server. Each LUN is allocated to only one server.
You can use this grouping strategy to logically group the iSCSI SAN storage for a given department or service category in the data center.
Each node of a cluster is listed as an initiator. All of the shared target LUNs are allocated to each node. All nodes are attached to the devices, but for most file systems, the cluster software locks a device for access and mounts it on only one node at a time. Shared file systems (such as OCFS2) make it possible for multiple nodes to concurrently mount the same file structure and to open the same files with read and write access.
You can use this grouping strategy to logically group the iSCSI SAN storage for a given server cluster.
Select an initiator entry, click
, specify the authentication settings for the initiator, then click to save the settings.You can require
, or you can configure , , or both. You can specify only one user name and password pair for each initiator. The credentials can be different for incoming and outgoing authentication for an initiator. The credentials can be different for each initiator.Repeat the previous steps for each iSCSI initiator that can access this target group.
After the initiator assignments are configured, click
.
Click
to save and apply the settings.
15.2.5 Modifying an iSCSI LIO Target Group #
You can modify an existing iSCSI LIO target group as follows:
Add or remove target LUN devices from a target group
Add or remove initiators for a target group
Modify the initiator LUN-to-target LUN mappings for an initiator of a target group
Modify the user name and password credentials for an initiator authentication (incoming, outgoing, or both)
To view or modify the settings for an iSCSI LIO target group:
Start YaST and launch
› .Switch to the
tab.Select the iSCSI LIO target group to be modified, then click
.On the Modify iSCSI Target LUN Setup page, add LUNs to the target group, edit the LUN assignments, or remove target LUNs from the group. After all desired changes have been made to the group, click
.For option information, see Modify iSCSI Target: Options.
On the Modify iSCSI Target Initiator Setup page, configure information for the initiators that are permitted to access LUNs in the target group. After all desired changes have been made to the group, click
.Click
to save and apply the settings.
15.2.6 Deleting an iSCSI LIO Target Group #
Deleting an iSCSI LIO target group removes the definition of the group, and the related setup for initiators, including LUN mappings and authentication credentials. It does not destroy the data on the partitions. To give initiators access again, you can allocate the target LUNs to a different or new target group, and configure the initiator access for them.
Start YaST and launch
› .Switch to the
tab.Select the iSCSI LIO target group to be deleted, then click
.When you are prompted, click
to confirm the deletion, or click to cancel it.Click
to save and apply the settings.
15.3 Configuring iSCSI Initiator #
The iSCSI initiator can be used to connect to any iSCSI target. This is not restricted to the iSCSI target solution explained in Section 15.2, “Setting Up an iSCSI LIO Target Server”. The configuration of iSCSI initiator involves two major steps: the discovery of available iSCSI targets and the setup of an iSCSI session. Both can be done with YaST.
15.3.1 Using YaST for the iSCSI Initiator Configuration #
The iSCSI Initiator Overview in YaST is divided into three tabs:
- Service:
The
tab can be used to enable the iSCSI initiator at boot time. It also offers to set a unique and an iSNS server to use for the discovery.- Connected Targets:
The
tab gives an overview of the currently connected iSCSI targets. Like the tab, it also gives the option to add new targets to the system.- Discovered Targets:
The
tab provides the possibility of manually discovering iSCSI targets in the network.
15.3.1.1 Configuring the iSCSI Initiator #
Start YaST and launch
› .Switch to the
tab.Under
, define what to do if there is a configuration change. Bear in mind that available options depend on the service current status.The
option keeps the service in the same status.In the
menu specify action that will take place after reboot:Specify or verify the
.Specify a well-formed iSCSI qualified name (IQN) for the iSCSI initiator on this server. The initiator name must be globally unique on your network. The IQN uses the following general format:
iqn.yyyy-mm.com.mycompany:n1:n2
where n1 and n2 are alphanumeric characters. For example:
iqn.1996-04.de.suse:01:a5dfcea717a
The
is automatically completed with the corresponding value from the/etc/iscsi/initiatorname.iscsi
file on the server.If the server has iBFT (iSCSI Boot Firmware Table) support, the
is completed with the corresponding value in the IBFT, and you are not able to change the initiator name in this interface. Use the BIOS Setup to modify it instead. The iBFT is a block of information containing various parameters useful to the iSCSI boot process, including iSCSI target and initiator descriptions for the server.Use either of the following methods to discover iSCSI targets on the network.
iSNS: To use iSNS (Internet Storage Name Service) for discovering iSCSI targets, continue with Section 15.3.1.2, “Discovering iSCSI Targets by Using iSNS”.
Discovered Targets: To discover iSCSI target devices manually, continue with Section 15.3.1.3, “Discovering iSCSI Targets Manually”.
15.3.1.2 Discovering iSCSI Targets by Using iSNS #
Before you can use this option, you must have already installed and configured an iSNS server in your environment. For information, see Chapter 14, iSNS for Linux.
In YaST, select
, then select the tab.Specify the IP address of the iSNS server and port. The default port is 3205.
Click
to save and apply your changes.
15.3.1.3 Discovering iSCSI Targets Manually #
Repeat the following process for each of the iSCSI target servers that you want to access from the server where you are setting up the iSCSI initiator.
In YaST, select
, then select the tab.Click
to open the iSCSI Initiator Discovery dialog.Enter the IP address and change the port if needed. The default port is 3260.
If authentication is required, deselect
, then specify the credentials for or .Click
to start the discovery and connect to the iSCSI target server.If credentials are required, after a successful discovery, use
to activate the target.You are prompted for authentication credentials to use the selected iSCSI target.
Click
to finish the configuration.The target now appears in
and the virtual iSCSI device is now available.Click
to save and apply your changes.You can find the local device path for the iSCSI target device by using the
lsscsi
command.
15.3.1.4 Setting the Start-up Preference for iSCSI Target Devices #
In YaST, select
, then select the tab to view a list of the iSCSI target devices that are currently connected to the server.Select the iSCSI target device that you want to manage.
Click
to modify the setting:Automatic: This option is used for iSCSI targets that are to be connected when the iSCSI service itself starts up. This is the typical configuration.
Onboot: This option is used for iSCSI targets that are to be connected during boot; that is, when root (
/
) is on iSCSI. As such, the iSCSI target device will be evaluated from the initrd on server boots. This option is ignored on platforms that cannot boot from iSCSI, such as IBM Z. Therefore it should not be used on these platforms; use instead.Click
to save and apply your changes.
15.3.2 Setting Up the iSCSI Initiator Manually #
Both the discovery and the configuration of iSCSI connections require a
running iscsid. When running the discovery the first time, the internal
database of the iSCSI initiator is created in the directory
/etc/iscsi/
.
If your discovery is password protected, provide the authentication
information to iscsid. Because the internal database does not exist when
doing the first discovery, it cannot be used now. Instead, the
configuration file /etc/iscsid.conf
must be edited to
provide the information. To add your password information for the
discovery, add the following lines to the end of
/etc/iscsid.conf
:
discovery.sendtargets.auth.authmethod = CHAP discovery.sendtargets.auth.username = USERNAME discovery.sendtargets.auth.password = PASSWORD
The discovery stores all received values in an internal persistent database. In addition, it displays all detected targets. Run this discovery with the following command:
>
sudo
iscsiadm-m discovery --type=st --portal=TARGET_IP
The output should look like the following:
10.44.171.99:3260,1 iqn.2006-02.com.example.iserv:systems
To discover the available targets on an iSNS
server, use
the following command:
sudo iscsiadm --mode discovery --type isns --portal TARGET_IP
For each target defined on the iSCSI target, one line appears. For more information about the stored data, see Section 15.3.3, “The iSCSI Initiator Databases”.
The special --login
option of iscsiadm
creates all needed devices:
>
sudo
iscsiadm -m node -n iqn.2006-02.com.example.iserv:systems --login
The newly generated devices show up in the output of
lsscsi
and can now be mounted.
15.3.3 The iSCSI Initiator Databases #
All information that was discovered by the iSCSI initiator is stored in two
database files that reside in /etc/iscsi
. There is one
database for the discovery of targets and one for the discovered nodes.
When accessing a database, you first must select if you want to get your
data from the discovery or from the node database. Do this with the
-m discovery
and -m node
parameters of
iscsiadm
. Using iscsiadm
with one of
these parameters gives an overview of the stored records:
>
sudo
iscsiadm -m discovery 10.44.171.99:3260,1 iqn.2006-02.com.example.iserv:systems
The target name in this example is
iqn.2006-02.com.example.iserv:systems
. This name is
needed for all actions that relate to this special data set. To examine the
content of the data record with the ID
iqn.2006-02.com.example.iserv:systems
, use the following
command:
>
sudo
iscsiadm -m node --targetname iqn.2006-02.com.example.iserv:systems node.name = iqn.2006-02.com.example.iserv:systems node.transport_name = tcp node.tpgt = 1 node.active_conn = 1 node.startup = manual node.session.initial_cmdsn = 0 node.session.reopen_max = 32 node.session.auth.authmethod = CHAP node.session.auth.username = joe node.session.auth.password = ******** node.session.auth.username_in = EMPTY node.session.auth.password_in = EMPTY node.session.timeo.replacement_timeout = 0 node.session.err_timeo.abort_timeout = 10 node.session.err_timeo.reset_timeout = 30 node.session.iscsi.InitialR2T = No node.session.iscsi.ImmediateData = Yes ....
To edit the value of one of these variables, use the command
iscsiadm
with the update
operation. For
example, if you want iscsid to log in to the iSCSI target when it
initializes, set the variable node.startup
to the value
automatic
:
sudo iscsiadm -m node -n iqn.2006-02.com.example.iserv:systems \ -p ip:port --op=update --name=node.startup --value=automatic
Remove obsolete data sets with the delete
operation. If
the target iqn.2006-02.com.example.iserv:systems
is no
longer a valid record, delete this record with the following command:
>
sudo
iscsiadm -m node -n iqn.2006-02.com.example.iserv:systems \ -p ip:port --op=delete
Use this option with caution because it deletes the record without any additional confirmation prompt.
To get a list of all discovered targets, run the sudo iscsiadm -m
node
command.
15.4 Setting Up Software Targets Using targetcli-fb #
targetcli
is a shell for managing the configuration
of the LinuxIO (LIO) target subsystem. The shell can be called
interactively, or you can execute one command at a time, much like a
conventional shell. Similar to a conventional shell, you can traverse
the targetcli functional hierarchy using the cd
command
and list contents with the ls
command.
The available commands depend on the current directory. While each directory
has its own set of commands, there are also commands that are available in
all directories (for example, the cd
and
ls
commands).
targetcli
commands have the following format:
[DIRECTORY] command
[ARGUMENTS]
You can use the help
command in any directory to view a
list of available commands or information about any command in particular.
The targetcli
tool is part of the
targetcli-fb package. This package is available in the
official SUSE Linux Enterprise Server software repository, and it can be installed using
the following command:
>
sudo
zypper install targetcli-fb
After the targetcli-fb package has been installed,
enable the targetcli
service:
>
sudo
systemctl enable targetcli>
sudo
systemctl start targetcli
To switch to the targetcli shell, run the targetcli
as root:
>
sudo
targetcli
You can then run the ls
command to see the default
configuration.
/> ls o- / ............................ [...] o- backstores ................. [...] | o- block ..... [Storage Objects: 0] | o- fileio .... [Storage Objects: 0] | o- pscsi ..... [Storage Objects: 0] | o- ramdisk ... [Storage Objects: 0] | o- rbd ....... [Storage Objects: 0] o- iscsi ............... [Targets: 0] o- loopback ............ [Targets: 0] o- vhost ............... [Targets: 0] o- xen-pvscsi .......... [Targets: 0] />
As the output of the ls
command indicates, there are no
configured back-ends. So the first step is to configure one of the
supported software targets.
targetcli supports the following back-ends:
fileio
, local image fileblock
, block storage on a dedicated disk or partitionpscsi
, SCSI pass-through devicesramdisk
, memory-based back-endrbd
, Ceph RADOS block devices
To familiarize yourself with the functionality of targetcli, set up a local
image file as a software target using the create
command:
/backstores/fileio create test-disc /alt/test.img 1G
This creates a 1 GB test.img
image in the
specified location (in this case /alt
). Run
ls
, and you should see the following result:
/> ls o- / ........................................................... [...] o- backstores ................................................ [...] | o- block .................................... [Storage Objects: 0] | o- fileio ................................... [Storage Objects: 1] | | o- test-disc ... [/alt/test.img (1.0GiB) write-back deactivated] | | o- alua ...... .......................... [ALUA Groups: 1] | | o- default_tg_pt_gp .... [ALUA state: Active/optimized] | o- pscsi .................................... [Storage Objects: 0] | o- ramdisk .................................. [Storage Objects: 0] | o- rbd ...................................... [Storage Objects: 0] o- iscsi .............................................. [Targets: 0] o- loopback ........................................... [Targets: 0] o- vhost .............................................. [Targets: 0] o- xen-pvscsi ......................................... [Targets: 0] />
The output indicates that there is now a file-based backstore, under the
/backstores/fileio
directory, called
test-disc
, which is linked to the created file
/alt/test.img
. Note that the new backstore is not yet
activated.
The next step is to connect an iSCSI target front-end to the back-end
storage. Each target must have an IQN
(iSCSI Qualified
Name). The most commonly used IQN format is as follows:
iqn.YYYY-MM.NAMING-AUTHORITY:UNIQUE-NAME
The following parts of an IQN are required:
YYYY-MM, the year and month when the naming authority was established
NAMING-AUTHORITY, reverse-syntax of the Internet Domain Name of the naming authority
UNIQUE-NAME, a domain-unique name chosen by the naming authority
For example, for the domain open-iscsi.com
, the IQN can
be as follows:
iqn.2005-03.com.open-iscsi:UNIQUE-NAME
When creating an iSCSI target, the targetcli
command
allows you to assign your own IQN, as long as it follows the specified
format. You can also let the command create an IQN for you by omitting a
name when creating the target, for example:
/> iscsi/ create
Run the ls
command again:
/> ls o- / ............................................................... [...] o- backstores .................................................... [...] | o- block ........................................ [Storage Objects: 0] | o- fileio ....................................... [Storage Objects: 1] | | o- test-disc ....... [/alt/test.img (1.0GiB) write-back deactivated] | | o- alua ......................................... [ALUA Groups: 1] | | o- default_tg_pt_gp ............. [ALUA state: Active/optimized] | o- pscsi ........................................ [Storage Objects: 0] | o- ramdisk ...................................... [Storage Objects: 0] | o- rbd .......................................... [Storage Objects: 0] o- iscsi .................................................. [Targets: 1] | o- iqn.2003-01.org.linux-iscsi.e83.x8664:sn.8b35d04dd456 ... [TPGs: 1] | o- tpg1 ..................................... [no-gen-acls, no-auth] | o- acls ................................................ [ACLs: 0] | o- luns ................................................ [LUNs: 0] | o- portals .......................................... [Portals: 1] | o- 0.0.0.0:3260 ........................................... [OK] o- loopback ............................................... [Targets: 0] o- vhost .................................................. [Targets: 0] o- xen-pvscsi ............................................. [Targets: 0] />
The output shows the created iSCSI target node with its automatically
generated IQN
iqn.2003-01.org.linux-iscsi.e83.x8664:sn.8b35d04dd456
Note that targetcli
has also created and enabled the default target portal
group tpg1
. This is done because the variables
auto_add_default_portal
and
auto_enable_tpgt
at the root level are set to
true
by default.
The command also created the default portal with the
0.0.0.0
IPv4 wildcard. This means that any IPv4 address
can access the configured target.
The next step is to create a LUN (Logical Unit Number) for the iSCSI
target. The best way to do this is to let targetcli
assign its name and
number automatically. Switch to the directory of the
iSCSI target, and then use the create
command in the
lun
directory to assign a LUN to the backstore.
/> cd /iscsi/iqn.2003-01.org.linux-iscsi.e83.x8664:sn.8b35d04dd456/ /iscsi/iqn.2003-01.org.linux-iscsi.e83.x8664:sn.8b35d04dd456> cd tpg1 /iscsi/iqn.2003-01.org.linux-iscsi.e83.x8664:sn.8b35d04dd456/tpg1> luns/ create /backstores/fileio/test-disc
Run the ls
command to see the changes:
/iscsi/iqn.2003-01.org.linux-iscsi.e83.x8664:sn.8b35d04dd456/tpg1> ls o- tpg1 .............................................. [no-gen-acls, no-auth] o- acls ..................................................... [ACLs: 0] o- luns ..................................................... [LUNs: 1] | o- lun0 ....... [fileio/test-disc (/alt/test.img) (default_tg_pt_gp)] o- portals ............................................... [Portals: 1] o- 0.0.0.0:3260 ................................................ [OK]
There is now an iSCSI target that has a 1 GB file-based backstore. The
target has the
iqn.2003-01.org.linux-iscsi.e83.x8664:sn.8b35d04dd456
name, and it can be accessed from any network port of the system.
Finally, you need to ensure that initiators have access to the configured
target. One way to do this is to create an ACL rule for each initiator that
allows them to connect to the target. In this case, you must list each
desired initiator using its IQN. The IQNs of the existing initiators can be
found in the /etc/iscsi/initiatorname.iscsi
file. Use
the following command to add the desired initiator (in this case, it's
iqn.1996-04.de.suse:01:54cab487975b
):
/iscsi/iqn.2003-01.org.linux-iscsi.e83.x8664:sn.8b35d04dd456/tpg1> acls/ create iqn.1996-04.de.suse:01:54cab487975b Created Node ACL for iqn.1996-04.de.suse:01:54cab487975b Created mapped LUN 0. /iscsi/iqn.2003-01.org.linux-iscsi.e83.x8664:sn.8b35d04dd456/tpg1>
Alternatively, you can run the target in a demo mode with no access restrictions. This method is less secure, but it can be useful for demonstration purposes and running on closed networks. To enable the demo mode, use the following commands:
/iscsi/iqn.2003-01.org.linux-iscsi.e83.x8664:sn.8b35d04dd456/tpg1> set attribute generate_node_acls=1 /iscsi/iqn.2003-01.org.linux-iscsi.e83.x8664:sn.8b35d04dd456/tpg1> set attribute demo_mode_write_protect=0
The last step is to save the created configuration using the
saveconfig
command available in the root directory:
/> saveconfig /etc/target/example.json
If at some point you need to restore configuration from the saved file, you need to clear the current configuration first. Keep in mind that clearing the current configuration results in data loss unless you save your configuration first. Use the following command to clear and reload the configuration:
/> clearconfig As a precaution, confirm=True needs to be set /> clearconfig confirm=true All configuration cleared /> restoreconfig /etc/target/example.json Configuration restored from /etc/target/example.json />
To test whether the configured target is working, connect to it using the open-iscsi iSCSI initiator installed on the same system (replace HOSTNAME with the hostname of the local machine):
>
iscsiadm -m discovery -t st -p HOSTNAME
This command returns a list of found targets, for example:
192.168.20.3:3260,1 iqn.2003-01.org.linux-iscsi.e83.x8664:sn.8b35d04dd456
You can then connect to the listed target using the
login
iSCSI command. This makes the target available as
a local disk.
15.5 Using iSCSI Disks when Installing #
Booting from an iSCSI disk on AMD64/Intel 64 and IBM POWER architectures is supported when iSCSI-enabled firmware is used.
To use iSCSI disks during installation, it is necessary to add the following parameter to the boot parameter line:
withiscsi=1
During installation, an additional screen appears that provides the option to attach iSCSI disks to the system and use them in the installation process.
iSCSI devices will appear asynchronously during the
boot process. While the initrd guarantees that those devices are
set up correctly for the root file system, there are no such
guarantees for any other file systems or mount points like
/usr
. Hence any system mount points like
/usr
or /var
are not
supported. To use those devices, ensure correct
synchronization of the respective services and devices.
15.6 Troubleshooting iSCSI #
This section describes some known issues and possible solutions for iSCSI target and iSCSI initiator issues.
15.6.1 Portal Error When Setting Up Target LUNs on an iSCSI LIO Target Server #
When adding or editing an iSCSI LIO target group, you get an error:
Problem setting network portal IP_ADDRESS:3260
The /var/log/YasT2/y2log
log file contains the
following error:
find: `/sys/kernel/config/target/iscsi': No such file or directory
This problem occurs if the iSCSI LIO Target Server software is not
currently running. To resolve this issue, exit YaST, manually start iSCSI
LIO at the command line with systemctl start targetcli
,
then try again.
You can also enter the following to check if configfs
,
iscsi_target_mod
, and target_core_mod
are loaded. A sample response is shown.
>
sudo
lsmod | grep iscsi iscsi_target_mod 295015 0 target_core_mod 346745 4 iscsi_target_mod,target_core_pscsi,target_core_iblock,target_core_file configfs 35817 3 iscsi_target_mod,target_core_mod scsi_mod 231620 16 iscsi_target_mod,target_core_pscsi,target_core_mod,sg,sr_mod,mptctl,sd_mod, scsi_dh_rdac,scsi_dh_emc,scsi_dh_alua,scsi_dh_hp_sw,scsi_dh,libata,mptspi, mptscsih,scsi_transport_spi
15.6.2 iSCSI LIO Targets Are Not Visible from Other Computers #
If you use a firewall on the target server, you must open the iSCSI port that you are using to allow other computers to see the iSCSI LIO targets. For information, see Section 15.2.1, “iSCSI LIO Target Service Start-up and Firewall Settings”.
15.6.3 Data Packets Dropped for iSCSI Traffic #
A firewall might drop packets if it gets too busy. The default for the SUSE Firewall is to drop packets after three minutes. If you find that iSCSI traffic packets are being dropped, consider configuring the SUSE Firewall to queue packets instead of dropping them when it gets too busy.
15.6.4 Using iSCSI Volumes with LVM #
Use the troubleshooting tips in this section when using LVM on iSCSI targets.
15.6.4.1 Check if the iSCSI Initiator Discovery Occurs at Boot #
When you set up the iSCSI Initiator, ensure that you enable discovery at boot time so that udev can discover the iSCSI devices at boot time and set up the devices to be used by LVM.
15.6.4.2 Check that iSCSI Target Discovery Occurs at Boot #
Remember that udev
provides the default setup for
devices. Ensure that all of the applications that create devices are
started at boot time so that udev
can recognize and
assign devices for them at system start-up. If the application or service
is not started until later, udev
does not create the
device automatically as it would at boot time.
15.6.5 iSCSI Targets Are Mounted When the Configuration File Is Set to Manual #
When Open-iSCSI starts, it can mount the targets even if the
node.startup
option is set to manual in the
/etc/iscsi/iscsid.conf
file if you manually modified
the configuration file.
Check the
/etc/iscsi/nodes/TARGET_NAME/IP_ADDRESS,PORT/default
file. It contains a node.startup
setting that overrides
the /etc/iscsi/iscsid.conf
file. Setting the mount
option to manual by using the YaST interface also sets
node.startup = manual
in the
/etc/iscsi/nodes/TARGET_NAME/IP_ADDRESS,PORT/default
files.
15.7 iSCSI LIO Target Terminology #
- backstore
A physical storage object that provides the actual storage underlying an iSCSI endpoint.
- CDB (command descriptor block)
The standard format for SCSI commands. CDBs are commonly 6, 10, or 12 bytes long, though they can be 16 bytes or of variable length.
- CHAP (Challenge Handshake Authentication Protocol)
A point-to-point protocol (PPP) authentication method used to confirm the identity of one computer to another. After the Link Control Protocol (LCP) connects the two computers, and the CHAP method is negotiated, the authenticator sends a random Challenge to the peer. The peer issues a cryptographically hashed Response that depends upon the Challenge and a secret key. The authenticator verifies the hashed Response against its own calculation of the expected hash value, and either acknowledges the authentication or terminates the connection. CHAP is defined in the RFC 1994.
- CID (connection identifier)
A 16‐bit number, generated by the initiator, that uniquely identifies a connection between two iSCSI devices. This number is presented during the login phase.
- endpoint
The combination of an iSCSI Target Name with an iSCSI TPG (IQN + Tag).
- EUI (extended unique identifier)
A 64‐bit number that uniquely identifies every device in the world. The format consists of 24 bits that are unique to a given company, and 40 bits assigned by the company to each device it builds.
- initiator
The originating end of an SCSI session. Typically a controlling device such as a computer.
- IPS (Internet Protocol storage)
The class of protocols or devices that use the IP protocol to move data in a storage network. FCIP (Fibre Channel over Internet Protocol), iFCP (Internet Fibre Channel Protocol), and iSCSI (Internet SCSI) are all examples of IPS protocols.
- IQN (iSCSI qualified name)
A name format for iSCSI that uniquely identifies every device in the world (for example:
iqn.5886.com.acme.tapedrive.sn‐a12345678
).- ISID (initiator session identifier)
A 48‐bit number, generated by the initiator, that uniquely identifies a session between the initiator and the target. This value is created during the login process, and is sent to the target with a Login PDU.
- MCS (multiple connections per session)
A part of the iSCSI specification that allows multiple TCP/IP connections between an initiator and a target.
- MPIO (multipath I/O)
A method by which data can take multiple redundant paths between a server and storage.
- network portal
The combination of an iSCSI endpoint with an IP address plus a TCP (Transmission Control Protocol) port. TCP port 3260 is the port number for the iSCSI protocol, as defined by IANA (Internet Assigned Numbers Authority).
- SAM (SCSI architectural model)
A document that describes the behavior of SCSI in general terms, allowing for different types of devices communicating over various media.
- target
The receiving end of an SCSI session, typically a device such as a disk drive, tape drive, or scanner.
- target group (TG)
A list of SCSI target ports that are all treated the same when creating views. Creating a view can help simplify LUN (logical unit number) mapping. Each view entry specifies a target group, host group, and a LUN.
- target port
The combination of an iSCSI endpoint with one or more LUNs.
- target port group (TPG)
A list of IP addresses and TCP port numbers that determines which interfaces a specific iSCSI target will listen to.
- target session identifier (TSID)
A 16‐bit number, generated by the target, that uniquely identifies a session between the initiator and the target. This value is created during the login process, and is sent to the initiator with a Login Response PDU (protocol data units).
15.8 Additional Information #
The iSCSI protocol has been available for several years. There are many reviews comparing iSCSI with SAN solutions, benchmarking performance, and there also is documentation describing hardware solutions. For more information, see the Open-iSCSI project home page at http://www.open-iscsi.com/.
Additionally, see the man pages for iscsiadm
,
iscsid
, and the example configuration file
/etc/iscsid.conf
.
16 Fibre Channel Storage over Ethernet Networks: FCoE #
Many enterprise data centers rely on Ethernet for their LAN and data traffic, and on Fibre Channel networks for their storage infrastructure. Open Fibre Channel over Ethernet (FCoE) Initiator software allows servers with Ethernet adapters to connect to a Fibre Channel storage subsystem over an Ethernet network. This connectivity was previously reserved exclusively for systems with Fibre Channel adapters over a Fibre Channel fabric. The FCoE technology reduces complexity in the data center by aiding network convergence. This helps to preserve your existing investments in a Fibre Channel storage infrastructure and to simplify network management.
Open-FCoE allows you to run the Fibre Channel protocols on the host, instead
of on proprietary hardware on the host bus adapter. It is targeted for 10
Gbps (gigabit per second) Ethernet adapters, but can work on any Ethernet
adapter that supports pause frames. The initiator software provides a Fibre
Channel protocol processing module and an Ethernet-based transport module.
The Open-FCoE module acts as a low-level driver for SCSI. The Open-FCoE
transport uses net_device
to send and receive packets.
Data Center Bridging (DCB) drivers provide the quality of service for FCoE.
FCoE is an encapsulation protocol that moves the Fibre Channel protocol traffic over Ethernet connections without changing the Fibre Channel frame. This allows your network security and traffic management infrastructure to work the same with FCoE as it does with Fibre Channel.
You might choose to deploy FCoE in your enterprise if the following conditions exist:
Your enterprise already has a Fibre Channel storage subsystem and administrators with Fibre Channel skills and knowledge.
You are deploying 10 Gbps Ethernet in the network.
This section describes how to set up FCoE in your network.
16.1 Configuring FCoE Interfaces during the Installation #
The YaST installation for SUSE Linux Enterprise Server allows you to configure FCoE disks
during the operating system installation if FCoE is enabled at the switch
for the connections between the server and the Fibre Channel storage
infrastructure. Some system BIOS types can automatically detect the FCoE
disks, and report the disks to the YaST Installation software. However,
automatic detection of FCoE disks is not supported by all BIOS types. To
enable automatic detection in this case, you can add the
withfcoe
option to the kernel command line when you begin
the installation:
withfcoe=1
When the FCoE disks are detected, the YaST installation offers the option to configure FCoE instances at that time. On the Disk Activation page, select Section 16.3, “Managing FCoE Services with YaST”.
to access the FCoE configuration. For information about configuring the FCoE interfaces, seeFCoE devices will appear asynchronously during the
boot process. While the initrd guarantees that those devices are
set up correctly for the root file system, there are no such
guarantees for any other file systems or mount points like
/usr
. Hence any system mount points like
/usr
or /var
are not
supported. To use those devices, ensure correct
synchronization of the respective services and devices.
16.2 Installing FCoE and the YaST FCoE Client #
You can set up FCoE disks in your storage infrastructure by enabling FCoE at the switch for the connections to a server. If FCoE disks are available when the SUSE Linux Enterprise Server operating system is installed, the FCoE Initiator software is automatically installed at that time.
If the FCoE Initiator software and the YaST FCoE Client software are not installed, use the following procedure to manually install them with the following command:
>
sudo
zypper in yast2-fcoe-client fcoe-utils
Alternatively, use the YaST Software Manager to install the packages listed above.
16.3 Managing FCoE Services with YaST #
You can use the YaST FCoE Client Configuration option to create,
configure, and remove FCoE interfaces for the FCoE disks in your Fibre
Channel storage infrastructure. To use this option, the FCoE Initiator
service (the fcoemon
daemon) and the
Link Layer Discovery Protocol agent daemon
(llpad
) must be installed and
running, and the FCoE connections must be enabled at the FCoE-capable
switch.
Launch YaST and select
› .On the
tab, view or modify the FCoE service and Lldpad (Link Layer Discovery Protocol agent daemon) service start time as necessary.FCoE Service Start: Specifies whether to start the Fibre Channel over Ethernet service
fcoemon
daemon at the server boot time or manually. The daemon controls the FCoE interfaces and establishes a connection with thellpad
daemon. The values are (default) or .Lldpad Service Start: Specifies whether to start the Link Layer Discovery Protocol agent
llpad
daemon at the server boot time or manually. Thellpad
daemon informs thefcoemon
daemon about the Data Center Bridging features and the configuration of the FCoE interfaces. The values are (default) or .
If you modify a setting, click
to save and apply the change.On the
tab, view information about all detected network adapters on the server, including information about VLAN and FCoE configuration. You can also create an FCoE VLAN interface, change settings for an existing FCoE interface, or remove an FCoE interface.Use the
column to determine whether FCoE is available or not:- Interface Name
If a name is assigned to the interface, such as
eth4.200
, FCoE is available on the switch, and the FCoE interface is activated for the adapter.- Not Configured:
If the status is
, FCoE is enabled on the switch, but an FCoE interface has not been activated for the adapter. Select the adapter, then click to activate the interface on the adapter.- Not Available:
If the status is
, FCoE is not possible for the adapter because FCoE has not been enabled for that connection on the switch.
To set up an FCoE-enabled adapter that has not yet been configured, select it and click
. Confirm the query with .The adapter is now listed with an interface name in the
column.To change the settings for an adapter that is already configured, select it from the list, then click
.The following options can be configured:
Enable or disable the creation of FCoE instances for the adapter.
Specifies whether Data Center Bridging is required for the adapter (usually this is the case).
Specifies whether the
fcoemon
daemon creates the VLAN interfaces automatically.
If you modify a setting, click
to save and apply the change. The settings are written to the/etc/fcoe/cfg-ethX
file. Thefcoemon
daemon reads the configuration files for each FCoE interface when it is initialized.To remove an interface that is already configured, select it from the list. Click
and to confirm. The FCoE Interface value changes to .On the
tab, view or modify the general settings for the FCoE system service. You can enable or disable debugging messages from the FCoE service script and thefcoemon
daemon and specify whether messages are sent to the system log.Click
to save and apply changes.
16.4 Configuring FCoE with commands #
The following steps reqire using the fipvlan
command. If
the command is not installed, install it by running:
>
sudo
zypper in fcoe-utils
To discover and configure all Ethernet interfaces, proceed as follows:
Open the terminal.
To discover all available Ethernet interfaces, run the following command:
>
sudo
fipvlan -aFor each Ethernet interface where FCoe offload is configured, run the following command:
>
sudo
fipvlan -c -s ETHERNET_INTERFACEThe command creates a network interface if it does not exist and starts the
Open-FCoE
initiator on the discovered FCoE VLAN.
16.5 Managing FCoE Instances with the FCoE Administration Tool #
The fcoeadm
utility is the Fibre Channel over Ethernet
(FCoE) management tool. It can be used to create, destroy, and reset an FCoE
instance on a given network interface. The fcoeadm
utility sends commands to a running
fcoemon
process via a socket
interface. For information about fcoemon
, see the
man 8 fcoemon
.
The fcoeadm
utility allows you to query the FCoE
instances about the following:
Interfaces
Target LUNs
Port statistics
The fcoeadm
utility is part of the
fcoe-utils
package. The general syntax for the command
looks like the following:
fcoeadm [-c|--create] [<ethX>] [-d|--destroy] [<ethX>] [-r|--reset] [<ethX>] [-S|--Scan] [<ethX>] [-i|--interface] [<ethX>] [-t|--target] [<ethX>] [-l|--lun] [<ethX>] [-s|--stats <ethX>] [<interval>] [-v|--version] [-h|--help]
Refer to man 8 fcoeadm
for details.
Examples#
fcoeadm -c eth2.101
Create an FCoE instance on eth2.101.
fcoeadm -d eth2.101
Destroy an FCoE instance on eth2.101.
fcoeadm -i eth3
Show information about all FCoE instances on interface
eth3
. If no interface is specified, information for all interfaces that have FCoE instances created will be shown. The following example shows information on connection eth0.201:>
sudo
fcoeadm -i eth0.201 Description: 82599EB 10-Gigabit SFI/SFP+ Network Connection Revision: 01 Manufacturer: Intel Corporation Serial Number: 001B219B258C Driver: ixgbe 3.3.8-k2 Number of Ports: 1 Symbolic Name: fcoe v0.1 over eth0.201 OS Device Name: host8 Node Name: 0x1000001B219B258E Port Name: 0x2000001B219B258E FabricName: 0x2001000573D38141 Speed: 10 Gbit Supported Speed: 10 Gbit MaxFrameSize: 2112 FC-ID (Port ID): 0x790003 State: Onlinefcoeadm -l eth3.101
Show detailed information about all LUNs discovered on connection eth3.101. If no connection is specified, information about all LUNs discovered on all FCoE connections will be shown.
fcoeadm -r eth2.101
Reset the FCoE instance on eth2.101.
fcoeadm -s eth3 3
Show statistical information about a specific eth3 port that has FCoE instances, at an interval of three seconds. The statistics are displayed one line per time interval. If no interval is given, the default of one second is used.
fcoeadm -t eth3
Show information about all discovered targets from a given eth3 port having FCoE instances. After each discovered target, any associated LUNs are listed. If no instance is specified, targets from all ports that have FCoE instances are shown. The following example shows information of targets from the eth0.201 connection:
>
sudo
fcoeadm -t eth0.201 Interface: eth0.201 Roles: FCP Target Node Name: 0x200000D0231B5C72 Port Name: 0x210000D0231B5C72 Target ID: 0 MaxFrameSize: 2048 OS Device Name: rport-8:0-7 FC-ID (Port ID): 0x79000C State: Online LUN ID Device Name Capacity Block Size Description ------ ----------- ---------- ---------- ---------------------------- 40 /dev/sdqi 792.84 GB 512 IFT DS S24F-R2840-4 (rev 386C) 72 /dev/sdpk 650.00 GB 512 IFT DS S24F-R2840-4 (rev 386C) 168 /dev/sdgy 1.30 TB 512 IFT DS S24F-R2840-4 (rev 386C)
16.6 Additional Information #
For information, see the follow documentation:
For information about the Open-FCoE service daemon, see the
fcoemon(8)
man page.For information about the Open-FCoE Administration tool, see the
fcoeadm(8)
man page.For information about the Data Center Bridging Configuration tool, see the
dcbtool(8)
man page.For information about the Link Layer Discovery Protocol agent daemon, see the
lldpad(8)
man page.For general information, see the Open-FCoE home page: http://www.open-fcoe.org/dokuwiki/start.
17 NVMe-oF #
This chapter describes how to set up an NVMe-oF host and target.
17.1 Overview #
NVM Express (NVMe) is an interface standard for accessing non-volatile storage, commonly SSD disks. NVMe supports much higher speeds and has a lower latency than SATA.
NVMe-oF is an architecture to access NVMe storage over different networking fabrics, for example RDMA, TCP or NVMe over Fibre Channel (FC-NVMe). The role of NVMe-oF is similar to iSCSI. To increase the fault-tolerance, NVMe-oF has a built-in support for multipathing. The NVMe-oF multipathing is not based on the traditional DM-Multipathing.
The NVMe host is the machine that connects to an NVMe target. The NVMe target is the machine that shares its NVMe block devices.
NVMe is supported on SUSE Linux Enterprise Server 15 SP2. There are Kernel modules available for the NVMe block storage and NVMe-oF target and host.
To see if your hardware requires any special consideration, refer to Section 17.4, “Special Hardware Configuration”.
17.2 Setting Up an NVMe-oF Host #
To use NVMe-oF, a target must be available with one of the supported networking methods. Supported are NVMe over Fibre Channel, TCP and RDMA. The following sections describe how to connect a host to an NVMe target.
17.2.1 Installing Command Line Client #
To use NVMe-oF, you need the nvme
command line
tool. Install it with zypper
:
>
sudo
zypper in nvme-cli
Use nvme --help
to list all available
subcommands. Man pages are available for nvme
subcommands. Consult them by executing man
nvme-SUBCOMMAND
. For example,
to view the man page for the discover
subcommand,
execute man nvme-discover
.
17.2.2 Discovering NVMe-oF Targets #
To list available NVMe subsystems on the NVMe-oF target, you need the discovery controller address and service ID.
>
sudo
nvme discover -t TRANSPORT -a DISCOVERY_CONTROLLER_ADDRESS -s SERVICE_ID
Replace TRANSPORT with the underlying
transport medium: loop
, rdma
, tcp
or
fc
. Replace
DISCOVERY_CONTROLLER_ADDRESS with the
address of the discovery controller. For RDMA and TCP this should be an
IPv4 address. Replace SERVICE_ID with
the transport service ID. If the service is IP based, like RDMA or TCP,
service ID specifies the port number. For Fibre Channel, the service
ID is not required.
The NVMe hosts only see the subsystems they are allowed to connect to.
Example:
>
sudo
nvme discover -t tcp -a 10.0.0.3 -s 4420
For the FC, the example looks as follows:
>
sudo
nvme discover --transport=fc \ --traddr=nn-0x201700a09890f5bf:pn-0x201900a09890f5bf \ --host-traddr=nn-0x200000109b579ef6:pn-0x100000109b579ef6
For more details, see man nvme-discover
.
17.2.3 Connecting to NVMe-oF Targets #
After you have identified the NVMe subsystem, you can connect it
with the nvme connect
command.
>
sudo
nvme connect -t transport -a DISCOVERY_CONTROLLER_ADDRESS -s SERVICE_ID -n SUBSYSTEM_NQN
Replace TRANSPORT with the underlying
transport medium: loop
, rdma
, tcp
or
fc
.
Replace DISCOVERY_CONTROLLER_ADDRESS with
the address of the discovery controller. For RDMA and TCP this should be an
IPv4 address.
Replace SERVICE_ID with the transport
service ID. If the service is IP based, like RDMA or TCP, this specifies
the port number.
Replace SUBSYSTEM_NQN with the NVMe
qualified name of the desired subsystem as found by the discovery
command. NQN is the abbreviation for
NVMe Qualified Name. The NQN must be unique.
Example:
>
sudo
nvme connect -t tcp -a 10.0.0.3 -s 4420 -n nqn.2014-08.com.example:nvme:nvm-subsystem-sn-d78432
Alternatively, use nvme connect-all
to connect
to all discovered namespaces. For advanced usage see
man nvme-connect
and man
nvme-connect-all
.
To make an NVMe over Fabrics subsytem available at boot, create a /etc/nvme/discovery.conf
file on the host with the parameters passed to the discover
command (as described in Section 17.2.2, “Discovering NVMe-oF Targets”. For example, if you use the discover
command as follows:
>
sudo
nvme connect -t tcp -a 10.0.0.3 -s 4420 -n nqn.2014-08.com.example:nvme:nvm-subsystem-sn-d78432
For the FC, the example looks as follows:
>
sudo
nvme connect --transport=fc \ --traddr=nn-0x201700a09890f5bf:pn-0x201900a09890f5bf \ --host-traddr=nn-0x200000109b579ef6:pn-0x100000109b579ef6 \ --nqn=nqn.2014-08.org.nvmexpress:uuid:1a9e23dd-466e-45ca-9f43-a29aaf47cb21
Add the parameters of the discover
command to the /etc/nvme/discovery.conf
file:
echo "-t tcp -a 10.0.0.3 -s 4420" | sudo tee -a /etc/nvme/discovery.conf
Then enable the
service:>
sudo
systemctl enable nvmf-autoconnect.service
17.2.4 Multipathing #
NVMe native multipathing is enabled by default. If the
CMIC
option in the controller identity settings is set,
the NVMe stack recognizes an NVME drive as a multipathed device by default.
To manage the multipathing, you can use the following:
nvme list-subsys
Prints the layout of the multipath devices.
multipath -ll
The command has a compatibility mode and displays NVMe multipath devices. Bear in mind that you need to enable the
enable_foreign
option to use the command. For details, refer to Section 18.13, “Miscellaneous options”.nvme-core.multipath=N
When the option is added as a boot parameter, the NVMe native multipathing will be disabled.
iostat
in multipath setups
The iostat
command might not show all
controllers that are listed by nvme list-subsys
.
By default, iostat
filters out all block devices
with no I/O. To make iostat
show
all devices, use:
iostat -p ALL
17.3 Setting Up an NVMe-oF Target #
17.3.1 Installing Command Line Client #
To configure an NVMe-oF target, you need the nvmetcli
command line
tool. Install it with zypper
:
>
sudo
zypper in nvmetcli
The current documentation for nvmetcli
is
available at http://git.infradead.org/users/hch/nvmetcli.git/blob_plain/HEAD:/Documentation/nvmetcli.txt.
17.3.2 Configuration Steps #
The following procedure provides an example of how to set up an NVMe-oF target.
The configuration is stored in a tree structure. Use the command
cd
to navigate. Use ls
to
list objects. You can create new objects with
create
.
Start the
nvmetcli
interactive shell:>
sudo
nvmetcli
Create a new port:
(nvmetcli)>
cd ports
(nvmetcli)>
create 1
(nvmetcli)>
ls 1/
o- 1 o- referrals o- subsystemsCreate an NVMe subsystem:
(nvmetcli)>
cd /subsystems
(nvmetcli)>
create nqn.2014-08.org.nvmexpress:NVMf:uuid:c36f2c23-354d-416c-95de-f2b8ec353a82
(nvmetcli)>
cd nqn.2014-08.org.nvmexpress:NVMf:uuid:c36f2c23-354d-416c-95de-f2b8ec353a82/
(nvmetcli)>
ls
o- nqn.2014-08.org.nvmexpress:NVMf:uuid:c36f2c23-354d-416c-95de-f2b8ec353a82 o- allowed_hosts o- namespacesCreate a new namespace and set an NVMe device to it:
(nvmetcli)>
cd namespaces
(nvmetcli)>
create 1
(nvmetcli)>
cd 1
(nvmetcli)>
set device path=/dev/nvme0n1
Parameter path is now '/dev/nvme0n1'.Enable the previously created namespace:
(nvmetcli)>
cd ..
(nvmetcli)>
enable
The Namespace has been enabled.Display the created namespace:
(nvmetcli)>
cd ..
(nvmetcli)>
ls
o- nqn.2014-08.org.nvmexpress:NVMf:uuid:c36f2c23-354d-416c-95de-f2b8ec353a82 o- allowed_hosts o- namespaces o- 1Allow all hosts to use the subsystem. Only do this in secure environments.
(nvmetcli)>
set attr allow_any_host=1
Parameter allow_any_host is now '1'.Alternatively, you can allow only specific hosts to connect:
(nvmetcli)>
cd nqn.2014-08.org.nvmexpress:NVMf:uuid:c36f2c23-354d-416c-95de-f2b8ec353a82/allowed_hosts/
(nvmetcli)>
create hostnqn
List all created objects:
(nvmetcli)>
cd /
(nvmetcli)>
ls
o- / o- hosts o- ports | o- 1 | o- referrals | o- subsystems o- subsystems o- nqn.2014-08.org.nvmexpress:NVMf:uuid:c36f2c23-354d-416c-95de-f2b8ec353a82 o- allowed_hosts o- namespaces o- 1Make the target available via TCP. Use
trtype=rdma
for RDMA:(nvmetcli)>
cd ports/1/
(nvmetcli)>
set addr adrfam=ipv4 trtype=tcp traddr=10.0.0.3 trsvcid=4420
Parameter trtype is now 'tcp'. Parameter adrfam is now 'ipv4'. Parameter trsvcid is now '4420'. Parameter traddr is now '10.0.0.3'.Alternatively, you can make it available with Fibre Channel:
(nvmetcli)>
cd ports/1/
(nvmetcli)>
set addr adrfam=fc trtype=fc traddr=nn-0x1000000044001123:pn-0x2000000055001123 trsvcid=none
Link the subsystem to the port:
(nvmetcli)>
cd /ports/1/subsystems
(nvmetcli)>
create nqn.2014-08.org.nvmexpress:NVMf:uuid:c36f2c23-354d-416c-95de-f2b8ec353a82
Now you can verify that the port is enabled using
dmesg
:#
dmesg ... [ 257.872084] nvmet_tcp: enabling port 1 (10.0.0.3:4420)
17.3.3 Back Up and Restore Target Configuration #
You can save the target configuration in a JSON file with the following commands:
>
sudo
nvmetcli
(nvmetcli)>
saveconfig nvme-target-backup.json
To restore the configuration, use:
(nvmetcli)>
restore nvme-target-backup.json
You can also wipe the current configuration:
(nvmetcli)>
clear
17.4 Special Hardware Configuration #
17.4.1 Overview #
Some hardware needs special configuration to work correctly. Skim the titles of the following sections to see if you are using any of the mentioned devices or vendors.
17.4.2 Broadcom #
If you are using the Broadcom Emulex LightPulse Fibre
Channel SCSI driver, add a Kernel configuration
parameter on the target and host for the lpfc
module:
>
sudo
echo "options lpfc lpfc_enable_fc4_type=3" > /etc/modprobe.d/lpfc.conf
Make sure that the Broadcom adapter firmware has at least version 11.4.204.33. Also make sure that you have the current versions of nvme-cli, nvmetcli and the Kernel installed.
To enable a Fibre Channel port as an NVMe target, an additional
module parameter needs to be configured:
lpfc_enable_nvmet=
COMMA_SEPARATED_WWPNS
. Enter the WWPN with a
leading 0x
, for example
lpfc_enable_nvmet=0x2000000055001122,0x2000000055003344
.
Only listed WWPNs will be configured for target mode. A Fibre
Channel port can either be configured as target
or as initiator.
17.4.3 Marvell #
FC-NVMe is supported on QLE269x and QLE27xx adapters. FC-NVMe support is enabled by default in the Marvell® QLogic® QLA2xxx Fibre Channel driver.
To confirm NVMe is enabled, run the following command:
>
cat /sys/module/qla2xxx/parameters/ql2xnvmeenable
A resulting 1
means NVMe is enabled, a
0
indicates it is disabled.
Next, ensure that the Marvell adapter firmware is at least version 8.08.204 by checking the output of the following command:
>
cat /sys/class/scsi_host/host0/fw_version
Last, ensure that the latest versions available for SUSE Linux Enterprise Server of nvme-cli, QConvergeConsoleCLI, and the Kernel are installed. You may, for example, run
#
zypper lu && zypper pchk
to check for updates and patches.
For more details on installation, please refer to the FC-NVMe sections in the following Marvell user guides:
17.5 More Information #
For more details about the abilities of the nvme
command,
refer to nvme nvme-help
.
The following links provide a basic introduction to NVMe and NVMe-oF:
18 Managing Multipath I/O for Devices #
This section describes how to manage failover and path load balancing for multiple paths between the servers and block storage devices by using Multipath I/O (MPIO).
18.1 Understanding Multipath I/O #
Multipathing is the ability of a server to communicate with the same physical or logical block storage device across multiple physical paths between the host bus adapters in the server and the storage controllers for the device, typically in Fibre Channel (FC) or iSCSI SAN environments.
Linux multipathing provides connection fault tolerance and can provide load balancing across the active connections. When multipathing is configured and running, it automatically isolates and identifies device connection failures, and reroutes I/O to alternate connections.
Multipathing provides fault tolerance against connection failures, but not against failures of the storage device itself. The latter is achieved with complementary techniques like mirroring.
18.1.1 Multipath terminology #
- Storage array
A hardware device with many disks and multiple fabrics connections (controllers) that provides SAN storage to clients. Storage arrays typically have RAID and failover features and support multipathing. Historically, active/passive (failover) and active/active (load-balancing) storage array configurations were distinguished. These concepts still exist but they are merely special cases of the concepts of path groups and access states supported by modern hardware.
- Host, host system
The computer running SUSE Linux Enterprise Server which acts as a client system for a storage array.
- Multipath map, multipath device
A set of path devices. It represents a storage volume on a storage array and is seen as a single block device by the host system.
- Path device
A member of a multipath map, typically a SCSI device. Each path device represents a unique connection between the host computer and the actual storage volume, for example, a logical unit from an iSCSI session.
- WWID
“World Wide Identifier”.
multipath-tools
uses the WWID to determine which low-level devices should be assembled into a multipath map. The WWID must be distinguished from the configurable map name (see Section 18.12, “Multipath device names and WWIDs”).- uevent, udev event
An event sent by the kernel to user space and processed by the
udev
subsystem. Uevents are generated when devices are added, removed, or change their properties.- Device mapper
A framework in the Linux kernel for creating virtual block devices. I/O operations to mapped devices are redirected to the underlying block devices. Device mappings may be stacked. The device mapper implements its own event signaling, also known as “device mapper events” or “dm events”.
- initramfs
The initial RAM file system, also referred to as “initial RAM disk” (initrd) for historical reasons (see Book “Administration Guide”, Chapter 12 “Introduction to the Boot Process”, Section 12.1 “Terminology”).
- ALUA
“Asymmetric Logical Unit Access”, a concept introduced with the SCSI standard SCSI-3. Storage volumes can be accessed via multiple ports, which are organized in port groups with different states (active, standby, etc.). ALUA defines SCSI commands to query the port groups and their states and change the state of a port group. Modern storage arrays that support SCSI usually support ALUA, too.
18.2 Hardware Support #
The multipathing drivers and tools are available on all architectures supported by SUSE Linux Enterprise Server. The generic, protocol-agnostic driver works with most multipath-capable storage hardware on the market. Some storage array vendors provide their own multipathing management tools. Consult the vendor’s hardware documentation to determine what settings are required.
18.2.1 Multipath implementations: device mapper and NVMe #
The traditional, generic implementation of multipathing under Linux uses the device mapper framework. For most device types like SCSI devices, device mapper multipathing is the only available implementation. Device mapper multipath is highly configurable and flexible.
The Linux NVM Express (NVMe) kernel subsystem implements multipathing natively in the kernel. This implementation creates less computational overhead for NVMe devices, which are typically fast devices with very low latencies. Native NVMe multipathing requires no user space component. Since SLE 15, native multipathing has been the default for NVMe multipath devices. For details, refer to Section 17.2.4, “Multipathing”.
This chapter documents device mapper multipath and its user-space
component, multipath-tools
.
multipath-tools
also has limited support for
native NVMe multipathing (see
Section 18.13, “Miscellaneous options”).
18.2.2 Storage array autodetection for multipathing #
Device mapper multipath is a generic technology. Multipath device detection requires only that the low-level (for example, SCSI) devices are detected by the kernel, and that device properties reliably identify multiple low-level devices as being different “paths” to the same volume rather than actually different devices.
The multipath-tools
package detects storage arrays by
their vendor and product names. It provides built-in configuration defaults
for a large variety of storage products. Consult the hardware documentation
of your storage array: some vendors provide specific recommendations for
Linux multipathing configuration.
If you need to apply changes to the built-in configuration for your storage array, read Section 18.8, “Multipath configuration”.
multipath-tools
has built-in presets for many storage
arrays. The existence of such presets for a given storage product
does not imply that the vendor of the storage product
has tested the product with dm-multipath
, nor
that the vendor endorses or supports the use of
dm-multipath
with the product. Always consult the
original vendor documentation for support-related questions.
18.2.3 Storage Arrays that Require Specific Hardware Handlers #
Some storage arrays require special commands for failover from one path to the other, or non-standard error-handling methods. These special commands and methods are implemented by hardware handlers in the Linux kernel. Modern SCSI storage arrays support the “Asymmetric Logical Unit Access” (ALUA) hardware handler defined in the SCSI standard. Besides ALUA, the SLE kernel contains hardware handlers for Netapp E-Series (RDAC), the Dell/EMC CLARiiON CX family of arrays, and legacy arrays from HP.
Since Linux kernel 4.4, the Linux kernel has automatically detected
hardware handlers for most arrays, including all arrays supporting ALUA.
The only requirement is that the device handler modules are loaded at the
time the respective devices are probed. The
multipath-tools
package ensures this by installing
appropriate configuration files. Once a device handler is attached to a
given device, it cannot be changed anymore.
18.3 Planning for Multipathing #
Use the guidelines in this section when planning your multipath I/O solution.
18.3.1 Prerequisites #
The storage array you use for the multipathed device must support multipathing. For more information, see Section 18.2, “Hardware Support”.
You need to configure multipathing only if multiple physical paths exist between host bus adapters in the server and host bus controllers for the block storage device.
For some storage arrays, the vendor provides its own multipathing software to manage multipathing for the array’s physical and logical devices. In this case, you should follow the vendor’s instructions for configuring multipathing for those devices.
When using multipathing in a virtualization environment, the multipathing is controlled in the host server environment. Configure multipathing for the device before you assign it to a virtual guest machine.
18.3.2 Multipath installation types #
We distinguish installation types by the way the root device is handled. Section 18.4, “Installing SUSE Linux Enterprise Server on multipath systems” describes how the different setups are created during and after installation.
18.3.2.1 Root file system on multipath (SAN-boot) #
The root file system is on a multipath device. This is typically the case for diskless servers that use SAN storage exclusively. On such systems, multipath support is required for booting, and multipathing must be enabled in the initramfs.
18.3.2.2 Root file system on a local disk #
The root file system (and possibly some other file systems) is on local storage, for example, on a directly attached SATA disk or local RAID, but the system additionally uses file systems in the multipath SAN storage. This system type can be configured in three different ways:
- Multipath setup for local disk
All block devices are part of multipath maps, including the local disk. The root device appears as a degraded multipath map with just one path. This configuration is created if multipathing was enabled during the initial system installation with YaST.
- Local disk is excluded from multipath
In this configuration, multipathing is enabled in the initramfs, but the root device is explicitly excluded from multipath (see Section 18.11.1, “The
blacklist
section inmultipath.conf
”). Procedure 18.1, “Disabling multipathing for the root disk after installation” describes how to set up this configuration.- Multipath disabled in the initramfs
This setup is created if multipathing was not enabled during the initial system installation with YaST. This configuration is rather fragile; consider using one of the other options instead.
18.3.3 Disk Management Tasks #
Use third-party SAN array management tools or the user interface of your storage array to create logical devices and assign them to hosts. Make sure to configure the host credentials correctly on both sides.
You can add or remove volumes to a running host, but detecting the changes may require rescanning SCSI targets and reconfiguring multipathing on the host. See Section 18.14.6, “Scanning for new devices without rebooting”.
On some disk arrays, the storage array manages the traffic through storage processors. One processor is active and the other one is passive until there is a failure. If you are connected to the passive storage processor, you might not see the expected LUNs, or you might see the LUNs but encounter I/O errors when you try to access them.
If a disk array has more than one storage processor, ensure that the SAN switch has a connection to the active storage processor that owns the LUNs you want to access.
18.3.4 Software RAID and complex storage stacks #
Multipathing is set up on top of basic storage devices such as SCSI disks. In a multi-layered storage stack, multipathing is always the bottom layer. Other layers such as software RAID, Logical Volume Management, block device encryption, etc. are layered on top of it. Therefore, for each device that has multiple I/O paths and that you plan to use in a software RAID, you must configure the device for multipathing before you attempt to create the software RAID device.
18.3.5 High-Availability Solutions #
High-availability solutions for clustering storage resources run on top of
the multipathing service on each node. Make sure that the configuration
settings in the /etc/multipath.conf
file on each node
are consistent across the cluster.
Make sure that multipath devices have the same name across all devices. Refer to Section 18.12, “Multipath device names and WWIDs” for details.
The Distributed Replicated Block Device (DRBD) high-availability solution for mirroring devices across a LAN runs on top of multipathing. For each device that has multiple I/O paths and that you plan to use in a DRDB solution, you must configure the device for multipathing before you configure DRBD.
Special care must be taken when using multipathing together with clustering
software that relies on shared storage for fencing, such as
pacemaker
with sbd
. See
Section 18.9.2, “Queuing policy on clustered servers” for details.
18.4 Installing SUSE Linux Enterprise Server on multipath systems #
No special installation parameters are required for the installation of SUSE Linux Enterprise Server on systems with multipath hardware.
18.4.1 Installing without connected multipath devices #
You may want to perform installation on a local disk, without configuring
the fabric and the storage first, with the intention to add multipath SAN
devices to the system later. In this case, the installation will proceed
like on a non-multipath system. After installation,
multipath-tools
will be installed, but the
systemd
service multipathd.service
will be disabled.
The system will be configured as described in
Multipath disabled in the initramfs in
Section 18.3.2.2, “Root file system on a local disk”. Before adding SAN
hardware, you will need to enable and start
multipathd.service
. We recommend creating a
blacklist
entry in the
/etc/multipath.conf
for the root device (see
Section 18.11.1, “The blacklist
section in multipath.conf
”).
18.4.2 Installing with connected multipath devices #
If multipath devices are connected to the system at installation time, YaST will detect them and display a pop-up window asking you whether multipath should be enabled before entering the partitioning stage.
If you select “No” at this prompt (not recommended), the installation will proceed as in Section 18.4.1, “Installing without connected multipath devices”. In the partitioning stage, do not use/edit devices that will later be part of a multipath map.
If you select “Yes” at the multipath prompt,
multipathd
will run during the installation. No device
will be added to the blacklist
section of
/etc/multipath.conf
, thus all SCSI and DASD devices,
including local disks, will appear as multipath devices in the partitioning
dialogs. After installation, all SCSI and DASD devices will be multipath
devices, as described in
Section 18.3.2.1, “Root file system on multipath (SAN-boot)”.
This procedure assumes that you installed on a local disk and enabled multipathing during installation, so that the root device is on multipath now, but you prefer to set up the system as described in Local disk is excluded from multipath in Section 18.3.2.2, “Root file system on a local disk”.
Check your system for
/dev/mapper/...
references to your local root device, and replace them with references that will still work if the device is not a multipath map anymore (see Section 18.12.4, “Referring to multipath maps”). If the following command finds no references, you do not need to apply changes:>
sudo
grep -rl /dev/mapper/ /etcSwitch to
by-uuid
persistent device policy fordracut
(see Section 18.7.4.2, “Persistent device names in the initramfs”):>
echo 'persistent_policy="by-uuid"' | \ sudo tee /etc/dracut.conf.d/10-persistent-policy.confDetermine the WWID of the root device:
>
multipathd show paths format "%i %d %w %s" 0:2:0:0 sda 3600605b009e7ed501f0e45370aaeb77f IBM,ServeRAID M5210 ...This command prints all paths devices with their WWIDs and vendor/product information. You will be able to identify the root device (here, the ServeRAID device) and note the WWID.
Create a blacklist entry in
/etc/multipath.conf
(see Section 18.11.1, “Theblacklist
section inmultipath.conf
”) with the WWID you just determined (do not apply these settings just yet):blacklist { wwid 3600605b009e7ed501f0e45370aaeb77f }
Rebuild the initramfs:
>
sudo
dracut -fReboot. Your system should boot with a non-multipath root disk.
18.5 Updating SLE on multipath systems #
When updating your system online, you can proceed as described in Book “Upgrade Guide”, Chapter 5 “Upgrading Online”.
The offline update of your system is similar to the fresh installation as
described in Section 18.4, “Installing SUSE Linux Enterprise Server on multipath systems”. There is no
blacklist
, thus if the user selects to enable multipath,
the root device will appear as a multipath device, even if it is normally
not. When dracut
builds the initramfs during the update
procedure, it sees a different storage stack as it would see on the booted
system. See Section 18.7.4.2, “Persistent device names in the initramfs” and
Section 18.12.4, “Referring to multipath maps”.
18.6 Multipath management tools #
The multipathing support in SUSE Linux Enterprise Server is based on the Device Mapper
Multipath module of the Linux kernel and the
multipath-tools
user space package.
The generic multipathing capability is handled by the Device Mapper Multipath (DM-MP) module. For details, refer to Section 18.6.1, “Device Mapper Multipath Module”.
The packages multipath-tools
and
kpartx
provide tools that handle
automatic path discovery and grouping. The tools are the following:
multipathd
The daemon to set up and monitor multipath maps, and a command-line client to communicate with the daemon process. See Section 18.6.2, “The
multipathd
daemon”.multipath
The command-line tool for multipath operations. See Section 18.6.3, “The
multipath
command”.kpartx
The command-line tool for managing “partitions” on multipath devices. See Section 18.7.3, “Partitions on multipath devices and
kpartx
”.mpathpersist
The command-line tool for managing SCSI persistent reservations. See Section 18.6.4, “SCSI persistent reservations and
mpathpersist
”.
18.6.1 Device Mapper Multipath Module #
The Device Mapper Multipath (DM-MP) module
dm-multipath.ko
provides the generic multipathing
capability for Linux. DM-MPIO is the preferred solution for multipathing on
SUSE Linux Enterprise Server for SCSI and DASD devices, and can be used for NVMe devices
as well.
Since SUSE Linux Enterprise Server 15, native NVMe multipathing (see
Section 18.2.1, “Multipath implementations: device mapper and NVMe”) has been
recommended for NVMe and used by default. To disable native NVMe
multipathing and use device mapper multipath instead (not
recommended), boot with the kernel parameter
nvme-core.multipath=0
.
The Device Mapper Multipath module handles the following tasks:
Distributing load over multiple paths inside the active path group.
Noticing I/O errors on path devices, and marking these as failed, so that no I/O will be sent to them.
Switching path groups when all paths in the active path group have failed.
Either failing or queuing I/O on the multipath device if all paths have failed, depending on configuration.
The following tasks are handled by the user-space components in the
multipath-tools
package, not by the Device Mapper
Multipath module:
Discovering devices representing different paths to the same storage device and assembling multipath maps from them.
Collecting path devices with similar properties into path groups.
Monitoring path devices actively for failure or reinstantiation.
Monitoring of addition and removal of path devices.
The Device Mapper Multipath module does not provide an easy-to-use user interface for setup and configuration.
For details about the components from the
multipath-tools
package, refer to
Section 18.6.2, “The multipathd
daemon”.
DM-MPIO protects against failures in the paths to the device, and not failures in the device itself, such as media errors. The latter kind of errors must be prevented by other means, such as replication.
18.6.2 The multipathd
daemon #
multipathd
is the most important part of a modern Linux
device mapper multipath setup. It is normally started through the systemd
service multipathd.service
(see
Section 18.7.1, “Enabling, starting, and stopping multipath services”).
multipathd
serves the following tasks (some of them
depend on the configuration):
On startup, detects path devices and sets up multipath maps from detected devices.
Monitors uevents and device mapper events, adding or removing path mappings to multipath maps as necessary and initiating failover or failback operations.
Sets up new maps on the fly when new path devices are discovered.
Checks path devices at regular intervals to detect failure, and tests failed paths to reinstate them if they become operational again.
When all paths fail,
multipathd
either fails the map, or switches the map device to queuing mode for a given time interval.Handles path state changes and switches path groups or regroups paths, as necessary.
Tests paths for “marginal” state, i.e. shaky fabrics conditions that cause path state flipping between operational and non-operational.
Handles SCSI persistent reservation keys for path devices if configured. See Section 18.6.4, “SCSI persistent reservations and
mpathpersist
”.
multipathd
also serves as a command-line client to
process interactive commands by sending them to the running daemon. The
general syntax to send commands to the daemon is as follows:
>
sudo
multipathd COMMAND
or
>
sudo
multipathd -k'COMMAND'
There is also an interactive mode that allows sending multiple subsequent commands:
>
sudo
multipathd -k
Many multipathd
commands have
multipath
equivalents. For example, multipathd
show topology
does the same thing as multipath
-ll
. The notable difference is that the multipathd command
inquires the internal state of the running multipathd
daemon, whereas multipath obtains information directly from the kernel and
I/O operations.
If the multipath daemon is running, we recommend making modifications to
the system by using the multipathd
commands. Otherwise,
the daemon may notice configuration changes and react to them. In some
situations, the daemon might even try to undo the applied changes.
multipath
automatically delegates certain possibly
dangerous commands, like destroying and flushing maps, to
multipathd
if a running daemon is detected.
The list below describes frequently used multipathd
commands:
- show topology
Shows the current map topology and properties. See Section 18.14.2, “Interpreting multipath I/O status”.
- show paths
Shows the currently known path devices.
- show paths format "FORMAT STRING"
Shows the currently known path devices using a format string. Use
show wildcards
to see a list of supported format specifiers.- show maps
Shows the currently configured map devices.
- show maps format FORMAT STRING
Shows the currently configured map devices using a format string. Use
show wildcards
to see a list of supported format specifiers.- show config local
Shows the current configuration that multipathd is using.
- reconfigure
Rereads configuration files, rescans devices, and sets up maps again. This is basically equivalent to a restart of
multipathd
. A few options cannot be modified without a restart. They are mentioned in the man pagemultipath.conf(5)
. Thereconfigure
command reloads only map devices that have changed in some way.- del map MAP DEVICE NAME
Unconfigure and delete the given map device and its partitions. MAP DEVICE NAME can be a device node name like
dm-0
, a WWID, or a map name. The command fails if the device is in use.- switchgroup map MAP DEVICE NAME group N
Switch to the path group with the given numeric index (starting at 1). This is useful for maps with manual failback (see Section 18.9, “Configuring policies for failover, queuing, and failback”).
Additional commands are available to modify path states, enable or disable
queuing, and more. See multipathd(8)
for details.
18.6.3 The multipath
command #
Even though multipath setup is mostly automatic and handled by
multipathd
, multipath
is still useful
for some administration tasks. Several examples of the command usage
follow:
- multipath
Detects path devices and and configures all multipath maps that it finds.
- multipath -d
Similar to
multipath
, but does not set up any maps (“dry run”).- multipath DEVICENAME
Configures a specific multipath device. DEVICENAME can denote a member path device by its device node name (
/dev/sdb
) or device number inmajor:minor
format. Alternatively, it can be the WWID or name of a multipath map.- multipath -f DEVICENAME
Unconfigures ("flushes") a multipath map and its partition mappings. The command will fail if the map or one of its partitions is in use. See above for possible values of DEVICENAME.
- multipath -F
Unconfigures ("flushes") all multipath maps and their partition mappings. The command will fail for maps in use.
- multipath -ll
Displays the status and topology of all currently configured multipath devices. See Section 18.14.2, “Interpreting multipath I/O status”.
- multipath -ll DEVICENAME
Displays the status of a specified multipath device. See above for possible values of DEVICENAME.
- multipath -t
Shows the internal hardware table and the active configuration of multipath. Refer to
multipath.conf(5)
for details about the configuration parameters.- multipath -T
Has a similar function as the
multipath -t
command but shows only hardware entries matching the hardware detected on the host.
The option -v
controls the verbosity of the output. The
provided value overrides the verbosity
option in
/etc/multipath.conf
. See
Section 18.13, “Miscellaneous options”.
18.6.4 SCSI persistent reservations and mpathpersist
#
The mpathpersist
utility is used to manage SCSI
persistent reservations on Device Mapper Multipath devices. Persistent
reservations serve to restrict access to SCSI Logical Units to certain SCSI
initiators. In multipath configurations, it is important to use the same
reservation keys for all I_T nexuses (paths) for a given volume; otherwise,
creating a reservation on one path device would cause I/O errors on other
paths.
Use this utility with the reservation_key
attribute in
the /etc/multipath.conf
file to set persistent
reservations for SCSI devices. If (and only if) this option is set, the
multipathd
daemon checks persistent reservations for
newly discovered paths or reinstated paths.
You can add the attribute to the defaults
section or the
multipaths
section of
multipath.conf
. For example:
multipaths { multipath { wwid 3600140508dbcf02acb448188d73ec97d alias yellow reservation_key 0x123abc } }
After setting the reservation_key
parameter for all
mpath devices applicable for persistent management, reload the
configuration using multipathd reconfigure
.
reservation_key file
”
If the special value reservation_key file
is used in
the defaults
section of
multipath.conf
, reservation keys can be managed
dynamically in the file /etc/multipath/prkeys
using
mpathpersist
.
This is the recommended way to handle persistent reservations with multipath maps. It is available from SUSE Linux Enterprise Server 12 SP4.
Use the command mpathpersist
to query and set persistent
reservations for multipath maps consisting of SCSI devices. Refer to the
manual page mpathpersist(8)
for details. The
command-line options are the same as those of the
sg_persist
from the sg3_utils
package. The sg_persist(8)
manual page explains
the semantics of the options in detail.
In the following examples, DEVICE denotes a
device mapper multipath device like
/dev/mapper/mpatha
. The commands below are listed with
long options for better readability. All options have single-letter
replacements, like in mpathpersist -oGS 123abc
DEVICE
.
- mpathpersist --in --read-keys DEVICE
Read the registered reservation keys for the device.
- mpathpersist --in --read-reservation DEVICE
Show existing reservations for the device.
- mpathpersist --out --register --param-sark=123abc DEVICE
Register a reservation key for the device. This will add the reservation key for all I_T nexuses (path devices) on the host.
- mpathpersist --out --reserve --param-rk=123abc --prout-type=5 DEVICE
Create a reservation of type 5 (“write exclusive - registrants only”) for the device, using the previously registered key.
- mpathpersist --out --release --param-rk=123abc --prout-type=5 DEVICE
Release a reservation of type 5 for the device.
- mpathpersist --out --register-ignore --param-sark=0 DEVICE
Delete a previously existing reservation key from the device.
18.7 Configuring the System for Multipathing #
18.7.1 Enabling, starting, and stopping multipath services #
To enable multipath services to start at boot time, run the following command:
>
sudo
systemctl enable multipathd
To manually start the service in the running system, enter:
>
sudo
systemctl start multipathd
To restart the service, enter:
>
sudo
systemctl restart multipathd
In most situations, restarting the service is not necessary. To simply have
multipathd
reload its configuration, run:
>
sudo
systemctl reload multipathd
To check the status of the service, enter:
>
sudo
systemctl status multipathd
To stop the multipath services in the current session, run:
>
sudo
systemctl stop multipathd multipathd.socket
Stopping the service does not remove existing multipath maps. To remove unused maps, run:
>
sudo
multipath -F
multipathd.service
enabled
We strongly recommend keeping multipathd.service
always enabled and running on systems with multipath hardware. The service
does support systemd
's socket activation mechanism, but
it is discouraged to rely on that. Multipath maps will not be set up
during boot if the service is disabled.
If you need to disable multipath despite the warning above, for example, because a third-party multipathing software is going to be deployed, proceed as follows. Be sure that the system uses no hard-coded references to multipath devices (see Section 18.15.2, “Understanding device referencing issues”).
To disable multipathing just for a single system
boot, use the kernel parameter
multipath=off
. This affects both the booted system and
the initramfs, which does not need to be rebuilt in this case.
To disable multipathd services permanently, so that they will not be started on future system boots, run the following commands:
>
sudo
systemctl disable multipathd multipathd.socket>
sudo
dracut --force --omit multipath
(Whenever you disable or enable the multipath services, rebuild the
initramfs
. See
Section 18.7.4, “Keeping the initramfs synchronized”.)
If you want to make sure multipath devices do not get set up,
even when running multipath
manually, add the following lines at the end of
/etc/multipath.conf
before rebuilding the initramfs:
blacklist { wwid .* }
18.7.2 Preparing SAN Devices for Multipathing #
Before configuring multipath I/O for your SAN devices, prepare the SAN devices, as necessary, by doing the following:
Configure and zone the SAN with the vendor’s tools.
Configure permissions for host LUNs on the storage arrays with the vendor’s tools.
If SUSE Linux Enterprise Server ships no driver for the host bus adapter (HBA), install a Linux driver from the HBA vendor. See the vendor’s specific instructions for more details.
If multipath devices are detected and
multipathd.service
is enabled, multipath maps should
be created automatically. If this does not happen,
Section 18.15.3, “Troubleshooting steps in emergency mode”
lists some shell commands that can be used to examine the situation. When
the LUNs are not seen by the HBA driver, check the zoning setup in the SAN.
In particular, check whether LUN masking is active and whether the LUNs are
correctly assigned to the server.
If the HBA driver can see LUNs, but no corresponding block devices are created, additional kernel parameters may be needed. See TID 3955167: Troubleshooting SCSI (LUN) Scanning Issues in the SUSE Knowledge base at https://www.suse.com/support/kb/doc.php?id=3955167.
18.7.3 Partitions on multipath devices and kpartx
#
Multipath maps can have partitions like their path devices. Partition table
scanning and device node creation for partitions is done in user space by
the kpartx
tool. kpartx
is
automatically invoked by udev rules; there is usually no need to run it
manually. See Section 18.12.4, “Referring to multipath maps” for ways to refer
to multipath partitions.
kpartx
The skip_kpartx
option in
/etc/multipath.conf
can be used to disable invocation
of kpartx
on selected multipath maps. This may be
useful on virtualization hosts, for example.
Partition tables and partitions on multipath devices can be manipulated as
usual, using YaST or tools like fdisk
or
parted
. Changes applied to the partition table will be
noted by the system when the partitioning tool exits. If this does not work
(usually because a device is busy), try multipathd
reconfigure
, or reboot the system.
18.7.4 Keeping the initramfs synchronized #
Make sure that the initial RAM file system (initramfs) and the booted system behave consistently regarding the use of multipathing for all block devices. Rebuild the initramfs after applying multipath configuration changes.
If multipathing is enabled in the system, it also needs to be enabled in
the initramfs
and vice versa. The only exception to
this rule is the option
Multipath disabled in the initramfs in
Section 18.3.2.2, “Root file system on a local disk”.
The multipath configuration must be synchronized between the booted system
and the initramfs. Therefore, if you change any of the files:
/etc/multipath.conf
,
/etc/multipath/wwids
,
/etc/multipath/bindings
, or other configuration files,
or udev rules related to device identification, rebuild initramfs using the
command:
>
sudo
dracut -f
If the initramfs
and the system are not synchronized,
the system will not boot properly, and the start-up procedure may result in
an emergency shell. See Section 18.15, “Troubleshooting MPIO” for
instructions on how to avoid or repair such a scenario.
18.7.4.1 Enabling or disabling multipathing in the initramfs #
Special care must be taken if the initramfs is rebuilt in non-standard
situations, for example, from a rescue system or after booting with the
kernel parameter multipath=off
.
dracut
will automatically include multipathing support
in the initramfs if and only if it detects that the root file system is on
a multipath device while the initramfs is being built. In such cases, it
is necessary to enable or disable multipathing explicitly.
To enable multipath support in the initramfs
, run the
command:
>
sudo
dracut --force --add multipath
To disable multipath support in initramfs
, run the
command:
>
sudo
dracut --force --omit multipath
18.7.4.2 Persistent device names in the initramfs #
When dracut
generates the initramfs, it must refer to
disks and partitions to be mounted in a persistent manner, to make sure
the system will boot correctly. When dracut
detects
multipath devices, it will use the DM-MP device names such as
/dev/mapper/3600a098000aad73f00000a3f5a275dc8-part1
for this purpose by default. This is good if the system
always runs in multipath mode. But if the system is
started without multipathing, as described in
Section 18.7.4.1, “Enabling or disabling multipathing in the initramfs”, booting with such an
initramfs will fail, because the /dev/mapper
devices
will not exist. See Section 18.12.4, “Referring to multipath maps” for another
possible problem scenario, and some background information.
To prevent this from happening, change dracut
's
persistent device naming policy by using the
--persistent-policy
option. We recommend setting the
by-uuid
use policy:
>
sudo
dracut --force --omit multipath --persistent-policy=by-uuid
See also Procedure 18.1, “Disabling multipathing for the root disk after installation” and Section 18.15.2, “Understanding device referencing issues”.
18.8 Multipath configuration #
The built-in multipath-tools
defaults work well for
most setups. If customizations are needed, a configuration file needs to be
created. The main configuration file is
/etc/multipath.conf
. In addition, files in
/etc/multipath/conf.d/
are taken into account. See
Section 18.8.2.1, “Additional configuration files and precedence rules” for additional
information.
Some storage vendors publish recommended values for multipath options in their documentation. These values often represent what the vendor has tested in their environment and found most suitable for the storage product. See the disclaimer in Section 18.2.2, “Storage array autodetection for multipathing”.
multipath-tools
has built-in defaults for many
storage arrays that are derived from the published vendor recommendations.
Run multipath -T
to see the current settings for your
devices and compare them to vendor recommendations.
18.8.1 Creating /etc/multipath.conf
#
It is recommended that you create a minimal
/etc/multipath.conf
that just contains those settings
you want to change. In many cases, you do not need to create
/etc/multipath.conf
at all.
If you prefer working with a configuration template that contains all possible configuration directives, run:
multipath -T >/etc/multipath.conf
See also Section 18.14.1, “Best practices for configuration”.
18.8.2 multipath.conf
syntax #
The /etc/multipath.conf
file uses a hierarchy of
sections, subsections, and option/value pairs.
White space separates tokens. Consecutive white space characters are collapsed into a single space, unless quoted (see below).
The hash (
#
) and exclamation mark (!
) characters cause the rest of the line to be discarded as a comment.Sections and subsections are started with a section name and an opening brace (
{
) on the same line, and end with a closing brace (}
) on a line on its own.Options and values are written on one line. Line continuations are unsupported.
Options and section names must be keywords. The allowed keywords are documented in
multipath.conf(5)
.Values may be enclosed in double quotes (
"
). They must be enclosed in quotes if they contain white space or comment characters. A double quote character inside a value is represented by a pair of double quotes (""
).The values of some options are POSIX regular expressions (see
regex(7)
). They are case sensitive and not anchored, so “bar
” matches “rhabarber
”, but not “Barbie”.
The following example illustrates the syntax:
section { subsection { option1 value option2 "complex value!" option3 "value with ""quoted"" word" } ! subsection end } # section end
18.8.2.1 Additional configuration files and precedence rules #
After /etc/multipath.conf
, the tools read files
matching the pattern /etc/multipath.conf.d/*.conf
.
The additional files follow the same syntax rules as
/etc/multipath.conf
. Sections and options can occur
multiple times. If the same option in the same
section is set in multiple files, or on multiple lines in the
same file, the last value takes precedence. Separate precedence rules
apply between multipath.conf
sections, see below.
18.8.3 multipath.conf
sections #
The /etc/multipath.conf
file is organized into the
following sections. Some options can occur in more than one section. See
multipath.conf(5)
for details.
- defaults
General default settings.
Important: Overriding built-in device propertiesBuilt-in hardware-specific device properties take precedence over the settings in the
defaults
section. Changes must therefore be made in thedevices
section or in theoverrides
section.- blacklist
Lists devices to ignore. See Section 18.11.1, “The
blacklist
section inmultipath.conf
”.- blacklist_exceptions
Lists devices to be multipathed even though they are matched by the blacklist. See Section 18.11.1, “The
blacklist
section inmultipath.conf
”.- devices
Settings specific to the storage controller. This section is a collection of
device
subsections. Values in this section override values for the same options in thedefaults
section, and the built-in settings ofmultipath-tools
.device
entries in thedevices
section are matched against the vendor and product of a device using regular expressions. These entries will be “merged”, setting all options from matching sections for the device. If the same option is set in multiple matchingdevice
sections, the last device entry takes precedence, even if it is less “specific” than preceding entries. This applies also if the matching entries appear in different configuration files (see Section 18.8.2.1, “Additional configuration files and precedence rules”). In the following example, a deviceSOMECORP STORAGE
will usefast_io_fail_tmo 15
.devices { device { vendor SOMECORP product STOR fast_io_fail_tmo 10 } device { vendor SOMECORP product .* fast_io_fail_tmo 15 } }
- multipaths
Settings for individual multipath devices. This section is a list of
multipath
subsections. Values override thedefaults
anddevices
sections.- overrides
Settings that override values from all other sections.
18.8.4 Applying multipath.conf
modifications #
To apply the configuration changes, run:
>
sudo
multipathd reconfigure
Do not forget to synchronize with the configuration in the initramfs. See Section 18.7.4, “Keeping the initramfs synchronized”.
multipath
Do not apply new settings with the multipath
command
while multipathd
is running. This may result in an
inconsistent and possibly broken setup.
It is possible to test modified settings first before they are applied, by running:
>
sudo
multipath -d -v2
This command shows new maps to be created with the proposed topology, but not whether maps will be removed/flushed. To obtain more information, run with increased verbosity:
>
sudo
multipath -d -v3 2>&1 | less
18.9 Configuring policies for failover, queuing, and failback #
The goal of multipath I/O is to provide connectivity fault tolerance between the storage system and the server. The desired default behavior depends on whether the server is a stand-alone server or a node in a high-availability cluster.
This section discusses the most important
multipath-tools
configuration parameters for
achieving fault tolerance.
- polling_interval
The time interval (in seconds) between health checks for path devices. The default is 5 seconds. Failed devices are checked at this time interval. For healthy devices, the time interval may be increased up to
max_polling_interval
seconds.- detect_checker
If this is set to
yes
(default, recommended),multipathd
automatically detects the best path checking algorithm.- path_checker
The algorithm used to check path state. If you need to enable the checker, disable
detect_checker
as follows:defaults { detect_checker no }
The following list contains only the most important algorithms. See
multipath.conf(5)
for the full list.- tur
Send TEST UNIT READY command. This is the default for SCSI devices with ALUA support.
- directio
Read a device sector using asynchronous I/O (aio).
- rdac
Device-specific checker for NetAPP E-Series and similar arrays.
- none
No path checking is performed.
- checker_timeout
If a device does not respond to a path checker command in the given time, it is considered failed. The default is the kernel's SCSI command timeout for the device (usually 30 seconds).
- fast_io_fail_tmo
If an error on the SCSI transport layer is detected (for example on a Fibre Channel remote port), the kernel transport layer waits for this amount of time (in seconds) for the transport to recover. After that, the path device fails with “transport offline” state. This is very useful for multipath, because it allows a quick path failover for a frequently occurring class of errors. The value must match typical time scale for reconfiguration in the fabric. The default value of 5 seconds works well for Fibre Channel. Other transports, like iSCSI, may require longer timeouts.
- dev_loss_tmo
If a SCSI transport endpoint (for example a Fibre Channel remote port) is not reachable any more, the kernel waits for this amount of time (in seconds) for the port to reappear until it removes the SCSI device node for good. Device node removal is a complex operation which is prone to race conditions or deadlocks and should best be avoided. We therefore recommend setting this to a high value. The special value
infinity
is supported. The default is 10 minutes. To avoid deadlock situations,multipathd
ensures that I/O queuing (seeno_path_retry
) is stopped beforedev_loss_tmo
expires.- no_path_retry
Determine what happens if all paths of a given multipath map have failed. The possible values are:
- fail
Fail I/O on the multipath map. This will cause I/O errors in upper layers such as mounted file systems. The affected file systems, and possibly the entire host, will enter degraded mode.
- queue
I/O on the multipath map is queued in the device mapper layer and sent to the device when path devices become available again. This is the safest option to avoid losing data, but it can have negative effects if the path devices do not get reinstated for a long time. Processes reading from the device will hang in uninterruptible sleep (
D
) state. Queued data occupies memory, which becomes unavailable for processes. Eventually, memory will be exhausted.- N
N is a positive integer. Keep the map device in queuing mode for N polling intervals. When the time elapses,
multipathd
fails the map device. Ifpolling_interval
is 5 seconds andno_path_retry
is 6,multipathd
will queue I/O for approximately 6 * 5s = 30s before failing I/O on the map device.
- flush_on_last_del
If set to
yes
and all path devices of a map are deleted (as opposed to just failed), fail all I/O in the map before removing it. The default isno
.- deferred_remove
If set to
yes
and all path devices of a map are deleted, wait for holders to close the file descriptors for the map device before flushing and removing it. If paths reappear before the last holder closed the map, the deferred remove operation will be cancelled. The default isno
.- failback
If a failed path device in an inactive path group recovers,
multipathd
reevaluates the path group priorities of all path groups (see Section 18.10, “Configuring path grouping and priorities”). After the reevaluation, the highest-priority path group may be one of the currently inactive path groups. This parameter determines what happens in this situation.Important: Observe vendor recommendationsThe optimal failback policy depends on the property of the storage device. It is therefore strongly encouraged to verify
failback
settings with the storage vendor.- manual
Nothing happens unless the administrator runs a
multipathd switchgroup
(see Section 18.6.2, “Themultipathd
daemon”).- immediate
The highest-priority path group is activated immediately. This is often beneficial for performance, especially on stand-alone servers, but it should not be used for arrays on which the change of the path group is a costly operation.
- followover
Like
immediate
, but only perform failback when the path that has just become active is the only healthy path in its path group. This is useful for cluster configurations: It keeps a node from automatically failing back when another node requested a failover before.- N
N is a positive integer. Wait for N polling intervals before activating the highest priority path group. If the priorities change again during this time, the wait period starts anew.
- eh_deadline
Set an approximate upper limit for the time (in seconds) spent in SCSI error handling if devices are unresponsive and SCSI commands time out without error response. When the deadline has elapsed, the kernel will perform a full HBA reset.
After modifying the /etc/multipath.conf
file, apply
your settings as described in
Section 18.8.4, “Applying multipath.conf
modifications”.
18.9.1 Queuing policy on stand-alone servers #
When you configure multipath I/O for a stand-alone server, a
no_path_retry
setting with value
queue
protects the server operating system from
receiving I/O errors as long as possible. It queues messages until a
multipath failover occurs. If “infinite” queuing is not desired
(see above), select a numeric value that is deemed high enough for the
storage paths to recover under ordinary circumstances (see above).
18.9.2 Queuing policy on clustered servers #
When you configure multipath I/O for a node in a high-availability cluster,
you want multipath to report the I/O failure to trigger the resource
failover instead of waiting for a multipath failover to be resolved. In
cluster environments, you must modify the no_path_retry
setting so that the cluster node receives an I/O error in
relation to the cluster verification process (recommended to be 50% of the
heartbeat tolerance) if the connection is lost to the storage system. In
addition, you want the multipath failback
to be set to
manual
or followover
to avoid a
ping-pong of resources because of path failures.
18.10 Configuring path grouping and priorities #
Path devices in multipath maps are grouped in path
groups, also called priority groups. Only
one path group receives I/O at any given time. multipathd
assigns priorities to path groups. Out of the path
groups with active paths, the group with the highest priority is activated
according to the configured failback policy for the map (see
Section 18.9, “Configuring policies for failover, queuing, and failback”).
The priority of a path group is the average of the priorities of the active
path devices in the path group. The priority of a path device is an integer
value calculated from the device properties (see the description of the
prio
option below).
This section describes the multipath.conf
configuration
parameters relevant for priority determination and path grouping.
- path_grouping_policy
Specifies the method used to combine paths into groups. Only the most important policies are listed here; see
multipath.conf(5)
for other less frequently used values.- failover
One path per path group. This setting is useful for traditional “active/passive” storage arrays.
- multibus
All paths in one path group. This is useful for traditional “active/active” arrays.
- group_by_prio
Path devices with the same path priority are grouped together. This option is useful for modern arrays that support asymmetric access states, like ALUA. Combined with the
alua
orsysfs
priority algorithms, the priority groups set up bymultipathd
will match the primary target port groups that the storage array reports through ALUA-related SCSI commands.
Using the same policy names, the path grouping policy for a multipath map can be changed temporarily with the command:
>
sudo
multipath -p POLICY_NAME MAP_NAME- marginal_pathgroups
If set to
on
orfpin
, “marginal” path devices are sorted into a separate path group. This is independent of the path grouping algorithm in use. See Section 18.13.1, “Handling unreliable (“marginal”) path devices”.- detect_prio
If this is set to
yes
(default, recommended),multipathd
automatically detects the best algorithm to set the priority for a storage device and ignores theprio
setting. In practice, this means using thesysfs
prio algorithm if ALUA support is detected.- prio
Determines the method to derive priorities for path devices. If you override this, disable
detect_prio
as follows:defaults { detect_prio no }
The following list contains only the most important methods. Several other methods are available, mainly to support legacy hardware. See
multipath.conf(5)
for the full list.- alua
Uses SCSI-3 ALUA access states to derive path priority values. The optional
exclusive_pref_bit
argument can be used to change the behavior for devices that have the ALUA “preferred primary target port group” (PREF) bit set:prio alua prio_args exclusive_pref_bit
If this option is set, “preferred” paths get a priority bonus over other active/optimized paths. Otherwise, all active/optimized paths are assigned the same priority.
- sysfs
Like
alua
, but instead of sending SCSI commands to the device, it obtains the access states fromsysfs
. This causes less I/O load thanalua
, but is not suitable for all storage arrays with ALUA support.- const
Uses a constant value for all paths.
- path_latency
Measures I/O latency (time from I/O submission to completion) on path devices, and assigns higher priority to devices with lower latency. See
multipath.conf(5)
for details. This algorithm is still experimental.- weightedpath
Assigns a priority to paths based on their name, serial number, Host:Bus:Target:Lun ID (HBTL), or Fibre Channel WWN. The priority value does not change over time. The method requires a
prio_args
argument, seemultipath.conf(5)
for details. For example:prio weightedpath prio_args "hbtl 2:.*:.*:.* 10 hbtl 3:.*:.*:.* 20 hbtl .* 1"
This assigns devices on SCSI host 3 a higher priority than devices on SCSI host 2, and all others a lower priority.
- prio_args
Some
prio
algorithms require extra arguments. These are specified in this option, with syntax depending on the algorithm. See above.- hardware_handler
The name of a kernel module that the kernel uses to activate path devices when switching path groups. This option has no effect with recent kernels because hardware handlers are autodetected. See Section 18.2.3, “Storage Arrays that Require Specific Hardware Handlers”.
- path_selector
The name of a kernel module that is used for load balancing between the paths of the active path group. The available choices depend on the kernel configuration. For historical reasons, the name must always be enclosed in quotes and followed by a “0” in
multipath.conf
, like this:path_selector "queue-length 0"
- service-time
Estimates the time pending I/O will need to complete on all paths, and selects the path with the lowest value. This is the default.
- historical-service-time
Estimates future service time based on the historical service time (about which it keeps a moving average) and the number of outstanding requests. Estimates the time pending I/O will need to complete on all paths, and selects the path with the lowest value.
- queue-length
Selects the path with the lowest number of currently pending I/O requests.
- round-robin
Switches paths in round-robin fashion. The number of requests submitted to a path before switching to the next one can be adjusted with the options
rr_min_io_rq
andrr_weight
.- io-affinity
This path selector currently does not work with
multipath-tools
.
After modifying the /etc/multipath.conf
file, apply
your settings as described in
Section 18.8.4, “Applying multipath.conf
modifications”.
18.11 Selecting devices for multipathing #
On systems with multipath devices, you might want to avoid setting up
multipath maps on some devices (typically local disks).
multipath-tools
offers various means for
configuring which devices should be considered multipath path devices.
In general, there is nothing wrong with setting up “degraded” multipath maps with just a single device on top of local disks. It works fine and requires no extra configuration. However, some administrators find this confusing or generally oppose this sort of unnecessary multipathing. Also, the multipath layer causes a slight performance overhead. See also Section 18.3.2.2, “Root file system on a local disk”.
After modifying the /etc/multipath.conf
file, apply
your settings as described in
Section 18.8.4, “Applying multipath.conf
modifications”.
18.11.1 The blacklist
section in multipath.conf
#
The /etc/multipath.conf
file can contain a
blacklist
section that lists all devices that should be
ignored by multipathd
and multipath
.
The following example illustrates possible ways of excluding devices:
blacklist { wwid 3600605b009e7ed501f0e45370aaeb77f 1 device { 2 vendor ATA product .* } protocol scsi:sas 3 property SCSI_IDENT_LUN_T10 4 devnode "!^dasd[a-z]*" 5 }
| |
This | |
Excluding by
This form is supported since SLES 15 SP1 and SLES 12 SP5. | |
This | |
Excluding devices by
The example illustrates special syntax that is only supported in the
|
By default, multipath-tools
ignores all devices
except SCSI, DASD, or NVMe. Technically, the built-in devnode exclude list
is this negated regular expression:
devnode !^(sd[a-z]|dasd[a-z]|nvme[0-9])
18.11.2 The blacklist exceptions
section in multipath.conf
#
Sometimes it is desired to configure only very specific devices for
multipathing. In this case, devices are excluded by default, and exceptions
are defined for devices that should be part of a multipath map. The
blacklist_exceptions
section exists for this purpose. It
is typically used like in the following example, which excludes everything
except storage with product string “NETAPP”:
blacklist { wwid .* } blacklist_exceptions { device { vendor ^NETAPP$ product .* } }
The blacklist_exceptions
section supports all methods
described for the blacklist
section above.
The property
directive in
blacklist_exceptions
is mandatory because every device
must have at least one of the “allowed”
udev properties to be considered a path device for multipath (the value of
the property does not matter). The built-in default for
property
is
property (SCSI_IDENT_|ID_WWN)
Only devices that have at least one udev property matching this regular expression will be included.
18.11.3 Other options affecting device selection #
Besides the blacklist
options, there are several other
settings in /etc/multipath.conf
that affect which
devices are considered multipath path devices.
- find_multipaths
This option controls the behavior of
multipath
andmultipathd
when a device that is not excluded is first encountered. The possible values are:- greedy
Every device non-excluded by
blacklist
in/etc/multipath.conf
is included. This is the default on SUSE Linux Enterprise. If this setting is active, the only way to prevent devices from being added to multipath maps is setting them as excluded.- strict
Every device is excluded, even if it is not present in the
blacklist
section of/etc/multipath.conf
, unless its WWID is listed in the file/etc/multipath/wwids
. It requires manual maintenance of the WWIDs file (see note below).- yes
Devices are included if they meet the conditions for
strict
, or if at least one other device with the same WWID exists in the system.- smart
If a new WWID is first encountered, it is temporarily marked as multipath path device.
multipathd
waits for some time for additional paths with the same WWID to appear. If this happens, the multipath map is set up as usual. Otherwise, when the timeout expires, the single device is released to the system as non-multipath device. The timeout is configurable with the optionfind_multipaths_timeout
.This option depends on
systemd
features which are only available on SUSE Linux Enterprise Server 15.
Note: Maintaining/etc/multipath/wwids
multipath-tools
keeps a record of previously setup multipath maps in the file/etc/multipath/wwids
(the “WWIDs file”). Devices with WWIDs listed in this file are considered multipath path devices. The file is important for multipath device selection for all values offind_multipaths
exceptgreedy
.If
find_multipaths
is set toyes
orsmart
,multipathd
adds WWIDs to/etc/multipath/wwids
after setting up new maps, so that these maps will be detected more quickly in the future.The WWIDs file can be manually modified:
>
sudo
multipath -a 3600a098000aad1e3000064e45f2c2355 1>
sudo
multipath -w /dev/sdf 2In the
strict
mode, this is the only way to add new multipath devices. After modifying the WWIDs file, runmultipathd reconfigure
to apply the changes. We recommend rebuilding the initramfs after applying changes to the WWIDs file (see Section 18.7.4, “Keeping the initramfs synchronized”).- allow_usb_devices
If this option is set to
yes
, USB storage devices are considered for multipathing. The default isno
.
18.12 Multipath device names and WWIDs #
multipathd
and multipath
internally
use WWIDs to identify devices. WWIDs are also used as map names by default.
For convenience, multipath-tools
supports assigning
simpler, easier memorizable names to multipath devices.
18.12.1 WWIDs and device Identification #
It is crucial for multipath operation to reliably detect devices that
represent paths to the same storage volume.
multipath-tools
uses the device's World Wide
Identification (WWID) for this purpose (sometimes also referred to as
Universally Unique ID (UUID) or Unique ID (UID — do not confuse with
“User ID”). The WWID of a map device is always the same as the
WWID of its path devices.
By default, WWIDs of path devices are inferred from udev properties of the devices, which are determined in udev rules, either by reading device attributes from the sysfs file system or by using specific I/O commands. To see the udev properties of a device, run:
>
udevadm info /dev/sdx
The udev properties used by multipath-tools
to
derive WWIDs are:
ID_SERIAL
for SCSI devices (do not confuse this with the device's “serial number”)ID_UID
for DASD devicesID_WWN
for NVMe devices
It is impossible to change the WWID of a multipath map which is in use. If the WWID of mapped path devices changes because of a configuration change, the map needs to be destroyed, and a new map needs to be set up with the new WWID. This cannot be done while the old map is in use. In extreme cases, data corruption may result from WWID changes. It must therefore be strictly avoided to apply configuration changes that would cause map WWIDs to change.
It is allowed to enable the uid_attrs
option in
/etc/multipath.conf
, see
Section 18.13, “Miscellaneous options”.
18.12.2 Setting aliases for multipath maps #
Arbitrary map names can be set in the multipaths
section
of /etc/multipath.conf
as follows:
multipaths { multipath { wwid 3600a098000aad1e3000064e45f2c2355 alias postgres } }
Aliases are expressive, but they need to be assigned to each map individually, which may be cumbersome on large systems.
18.12.3 Using autogenerated user-friendly names #
multipath-tools
also supports autogenerated
aliases, so-called “user-friendly names”. The naming scheme of
the aliases follows the pattern: mpathINDEX,
where INDEX is a lower case letter (starting
with a
). So the first autogenerated alias is
mpatha
, the next one is mpathb
,
mpathc
to mpathz
. After that follows
mpathaa
, mpathab
, and so on.
Map names are only useful if they are persistent.
multipath-tools
keeps track of the assigned names
in the file /etc/multipath/bindings
(the
“bindings file”). When a new map is created, the WWID is first
looked up in this file. If it is not found, the lowest available
user-friendly name is assigned to it.
Explicit aliases as discussed in Section 18.12.2, “Setting aliases for multipath maps” take precedence over user-friendly names.
The following options in /etc/multipath.conf
affect
user-friendly names:
- user_friendly_names
If set to
yes
, user-friendly names are assigned and used. Otherwise, the WWID is used as a map name unless an alias is configured.- alias_prefix
The prefix used to create user-friendly names,
mpath
by default.
For cluster operations, device names must be identical across all nodes in
the cluster. The multipath-tools
configuration
must be kept synchronized between nodes. If
user_friendly_names
is used,
multipathd
may modify the
/etc/multipath/bindings
file at runtime. Such
modifications must be replicated dynamically to all nodes. The same
applies to /etc/multipath/wwids
(see
Section 18.11.3, “Other options affecting device selection”).
It is possible to change map names at runtime. Use any of the methods
described in this section and run multipathd
reconfigure
, and the map names will change without disrupting
the system operation.
18.12.4 Referring to multipath maps #
Technically, multipath maps are Device Mapper devices, which have generic
names of the form /dev/dm-n
with an integer number n. These names are not
persistent. They should never be used to refer to the
multipath maps. udev
creates various symbolic links to
these devices, which are more suitable as persistent references. These
links differ with respect to their invariance against certain configuration
changes. The following typical example shows various symlinks all pointing
to the same device.
/dev/disk/by-id/dm-name-mpathb1 -> ../../dm-1 /dev/disk/by-id/dm-uuid-mpath-3600a098000aad73f00000a3f5a275dc82 -> ../../dm-1 /dev/disk/by-id/scsi-3600a098000aad73f00000a3f5a275dc83 -> ../../dm-1 /dev/disk/by-id/wwn-0x600a098000aad73f00000a3f5a275dc84 -> ../../dm-1 /dev/mapper/mpathb5 -> ../dm-1
These two links use the map name to refer to the map. Thus, the links will change if the map name changes, for example, if you enable or disable user-friendly names. | |
This link uses the device mapper UUID, which is the WWID used by
The device mapper UUID is the preferred form to ensure that
only multipath devices are referenced. For example,
the following line in filter = [ "a|/dev/disk/by-id/dm-uuid-mpath-.*|", "r|.*|" ] | |
These are links that would normally point to path devices. The multipath
device took them over, because it has a higher udev link priority (see
|
For partitions on multipath maps created
by the kpartx
tool, there are similar symbolic links,
derived from the parent device name or WWID and the partition number:
/dev/disk/by-id/dm-name-mpatha-part2 -> ../../dm-5 /dev/disk/by-id/dm-uuid-part2-mpath-3600a098000aad1e300000b4b5a275d45 -> ../../dm-5 /dev/disk/by-id/scsi-3600a098000aad1e300000b4b5a275d45-part2 -> ../../dm-5 /dev/disk/by-id/wwn-0x600a098000aad1e300000b4b5a275d45-part2 -> ../../dm-5 /dev/disk/by-partuuid/1c2f70e0-fb91-49f5-8260-38eacaf7992b -> ../../dm-5 /dev/disk/by-uuid/f67c49e9-3cf2-4bb7-8991-63568cb840a4 -> ../../dm-5 /dev/mapper/mpatha-part2 -> ../dm-5
Note that partitions often have by-uuid
links, too,
referring not to the device itself but to the file system it contains.
These links are often preferable. They are invariant even if the file
system is copied to a different device or partition.
When dracut
builds an initramfs, it creates hard-coded
references to devices in the initramfs, using
/dev/mapper/$MAP_NAME
references by default. These
hard-coded references will not be found during boot if the map names used
in the initramfs do not match the names used during building the
initramfs, causing boot failure. Normally this will not happen, because
dracut
will add all multipath configuration files to
the initramfs. But problems can occur if the initramfs is built from a
different environment, for example, in the rescue system or during an
offline update. To prevent this boot failure, change
dracut
's persistent_policy
setting,
as explained in Section 18.7.4.2, “Persistent device names in the initramfs”.
18.13 Miscellaneous options #
This section lists some useful multipath.conf
options
that were not mentioned so far. See
multipath.conf(5)
for a full list.
- verbosity
Controls the log verbosity of both
multipath
andmultipathd
. The command-line option-v
overrides this setting for both commands. The value can be between 0 (only fatal errors) and 4 (verbose logging). The default is 2.- uid_attrs
This option enables an optimization for processing udev events, so-called “uevent merging”. It is useful in environments in which hundreds of path devices may fail or reappear simultaneously. In order to make sure that path WWIDs do not change (see Section 18.12.1, “WWIDs and device Identification”), the value should be set exactly like this:
defaults { uid_attrs "sd:ID_SERIAL dasd:ID_UID nvme:ID_WWN" }
- skip_kpartx
If set to
yes
for a multipath device (default isno
), do not create partition devices on top of the given device (see Section 18.7.3, “Partitions on multipath devices andkpartx
”). Useful for multipath devices used by virtual machines. Previous SUSE Linux Enterprise Server releases achieved the same effect with the parameter “features 1 no_partitions
”.- max_sectors_kb
Limits the maximum amount of data sent in a single I/O request for all path devices of the multipath map.
- ghost_delay
On active/passive arrays, it can happen that passive paths (in “ghost” state) are probed before active paths. If the map was activated immediately and I/O was sent, this would cause a possibly costly path activation. This parameter specifies the time (in seconds) to wait for active paths of the map to appear before activating the map. The default is
no
(no ghost delay).- recheck_wwid
If set to
yes
(default isno
), double-checks the WWID of restored paths after failure, and removes them if the WWID has changed. This is a safety measure against data corruption.- enable_foreign
multipath-tools
provides a plugin API for other multipathing backends than Device Mapper multipath. The API supports monitoring and displaying information about the multipath topology using standard commands likemultipath -ll
. Modifying the topology is unsupported.The value of
enable_foreign
is a regular expression to match against foreign library names. The default value is “NONE
”.SUSE Linux Enterprise Server ships the
nvme
plugin, which adds support for the native NVMe multipathing (see Section 18.2.1, “Multipath implementations: device mapper and NVMe”). To enable thenvme
plugin, setdefaults { enable_foreign nvme }
18.13.1 Handling unreliable (“marginal”) path devices #
Unstable conditions in the fabric can cause path devices to behave
erratically. They exhibit frequent I/O errors, recover, and fail again.
Such path devices are also denoted “marginal” or
“shaky” paths. This section summarizes the options that
multipath-tools
provides to deal with this
problem.
If a path device exhibits a second failure (good → bad transition) before
marginal_path_double_failed_time
elapses after the
first failure, multipathd
starts monitoring the path at
a rate of 10 requests per second, for a monitoring period of
marginal_path_err_sample_time
. If the error rate during
the monitoring period exceeds
marginal_path_err_rate_threshold
, the path is
classified as marginal. After
marginal_path_err_recheck_gap_time
, the path
transitions to normal state again.
This algorithm is used if all four numeric
marginal_path_
parameters are set to a positive value,
and marginal_pathgroups
is not set to
fpin
. It is available since SUSE Linux Enterprise Server 15 SP1 and
SUSE Linux Enterprise Server 12 SP5.
- marginal_path_double_failed_time
Maximum time (in seconds) between two path failures that triggers path monitoring.
- marginal_path_err_sample_time
Length (in seconds) of the path monitoring interval.
- marginal_path_err_rate_threshold
Minimum error rate (per thousand I/Os).
- marginal_path_err_recheck_gap_time
Time (in seconds) to keep the path in marginal state.
A simpler algorithm using the parameters
san_path_err_threshold
,
san_path_err_forget_rate
, and
san_path_err_recovery time
is also available and
recommended for SUSE Linux Enterprise Server 15 (GA). See the “Shaky paths
detection” section in multipath.conf(5)
.
18.14 Best Practice #
18.14.1 Best practices for configuration #
The large number of configuration directives is daunting at first. Usually, you can get good results with an empty configuration, unless you are in a clustering environment.
Here are some general recommendations for stand-alone servers. They are not mandatory. See the documentation of the respective parameters in the previous sections for background information.
defaults { deferred_remove yes find_multipaths smart enable_foreign nvme marginal_pathgroups fpin # 15.4 only, if supported by fabric } devices { # A catch-all device entry. device { vendor .* product .* dev_loss_tmo infinity no_path_retry 60 # 5 minutes path_grouping_policy group_by_prio path_selector "historical-service-time 0" reservation_key file # if using SCSI persistent reservations } # Follow up with specific device entries below, they will take precedence. }
After modifying the /etc/multipath.conf
file, apply
your settings as described in
Section 18.8.4, “Applying multipath.conf
modifications”.
18.14.2 Interpreting multipath I/O status #
For a quick overview of the multipath subsystem, use multipath
-ll
or multipathd show topology
. The output of
these commands has the same format. The former command reads the kernel
state, while the latter prints the status of the multipath daemon. Normally
both states are equal. Here is an example of the output:
>
sudo
multipathd show topology mpatha1 (3600a098000aad1e300000b4b5a275d452) dm-03 NETAPP,INF-01-004 size=64G features='3 queue_if_no_path pg_init_retries 50'5 hwhandler='1 alua'6 wp=rw7 |-+- 8policy='historical-service-time 2'9 prio=5010 status=active11 | |-12 3:0:0:113 sdb 8:1614 active15 ready16 running17 | `- 4:0:0:1 sdf 8:80 active ready running `-+- policy='historical-service-time 2' prio=10 status=enabled `- 4:0:1:1 sdj 8:144 active ready running
The map name. | |
The map WWID (if different from the map name). | |
The device node name of the map device. | |
The vendor and product name. | |
A path group. The indented lines below the path group list the path devices that belong to it. | |
The path selector algorithm used by the path group. The "2" can be ignored. | |
The priority of the path group. | |
The status of the path group ( | |
A path device. | |
The bus ID of the device (here, a SCSI Host:Bus:Target:Lun ID). | |
The device node name and major/minor number of the path device. | |
The kernel device mapper state of the path ( | |
The multipath path device state (see below). | |
The state of the path device in the kernel. This is a device-type
specific value. For SCSI, it is either |
The multipath path device states are:
|
The path is healthy and up |
|
A passive path in an active/passive array |
|
The path is down or unreachable |
|
A checker command timed out |
|
Waiting for the completion of a path checker command |
|
Path reinstantiation is delayed to avoid "flapping" |
|
An unreliable path (emc path checker only) |
18.14.3 Using LVM2 on multipath devices #
LVM2 has built-in support for detecting multipath devices. It is activated
by default in /etc/lvm/lvm.conf
:
multipath_component_detection=1
This works reliably only if LVM2 is also configured to obtain information about device properties from udev:
external_device_info_source="udev"
It is also possible (although normally not necessary) to create a filter expression for LVM2 to ignore all devices except multipath devices. See Section 18.12.4, “Referring to multipath maps”.
18.14.4 Resolving Stalled I/O #
If all paths fail concurrently and I/O is queued, applications may stall for a long time. To resolve this, you can use the following procedure:
Enter the following command at a terminal prompt:
>
sudo
multipathd disablequeueing map MAPNAMEReplace
MAPNAME
with the correct WWID or mapped alias name for the device.This command immediately causes all queued I/O to fail and propagates the error to the calling application. File systems will observe I/O errors and switch to read-only mode.
Reactivate queuing by entering the following command:
>
sudo
multipathd restorequeueing MAPNAME
18.14.5 MD RAID on multipath devices #
MD RAID arrays on top of multipathing are set up automatically by the
system's udev rules. No special configuration in
/etc/mdadm.conf
is necessary.
18.14.6 Scanning for new devices without rebooting #
If your system has already been configured for multipathing and you need to
add storage to the SAN, you can use the
rescan-scsi-bus.sh
script to scan for the new devices.
The general syntax for the command follows:
>
sudo
rescan-scsi-bus.sh [-a] [-r] --hosts=2-3,5
Where the options have the following meaning:
- -a
the option ensures that all SCSI targets are scanned, otherwise only already existing targets will be scanned for new LUNs.
- -r
the option enables the removal of devices which have been removed on the storage side.
- --hosts
the option specifies the list of host bus adapters to scan (the default is to scan all).
Run rescan-scsi-bus.sh --help
for help on additional
options.
If multipathd
is running and new SAN devices are
discovered, they should be automatically set up as multipath maps according
to the configuration described in
Section 18.11, “Selecting devices for multipathing”.
In EMC PowerPath environments, do not use the
rescan-scsi-bus.sh
utility provided with the
operating system or the HBA vendor scripts for scanning the SCSI buses. To
avoid potential file system corruption, EMC requires that you follow the
procedure provided in the vendor documentation for EMC PowerPath for
Linux.
18.15 Troubleshooting MPIO #
If a system runs into emergency mode on a system with multipath, printing messages about missing devices, the reason is almost always one of these:
Inconsistent configuration of multipath device selection
Use of non-existing device references
18.15.1 Understanding device selection issues #
A block device can only either be part of a multipath map or be used
directly (mounted as file system, used as swap, LVM physical volume, or
otherwise). If a device is already mounted, an attempt by multipathd to
make it part of a multipath map will fail with a “Device or resource
busy” error. Vice-versa, the same error results if
systemd
attempts to mount a device which has already
been made part of a multipath map.
Storage device activation during boot is handled by a complex interaction
between systemd
, udev
,
multipathd
and some other tools.
udev
rules play a central role. They set device
properties that indicate to other subsystems how a device should be used.
The multipath-related udev rules set the following properties for devices
that are selected for multipathing:
SYSTEMD_READY=0 DM_MULTIPATH_DEVICE_PATH=1
Partition devices inherit these properties from their parents.
If these properties are not set correctly, if some tool does not respect
them, or if they get set too late, a race condition between
multipathd
and some other subsystem may result. Only one
of the contenders can win the race; the other one will see a “Device
or resource busy” error.
One problem in this context is that the tools of the LVM2 suite do not evaluate udev properties by default. They rely on their own logic for determining whether a device is a multipath component, which sometimes does not match the logic of the rest of the system. A workaround for this is described in Section 18.14.3, “Using LVM2 on multipath devices”.
Consider a system with multipathing where the root device is not
multipathed, and no devices are excluded from multipath (see
Multipath disabled in the initramfs in
Section 18.3.2.2, “Root file system on a local disk”). The root file
system is mounted in the initramfs. systemd
switches to
the root file system and multipathd
starts up. Because
the device is already mounted, multipathd
fails to set
up the multipath map for it. Because the root device is not configured in
blacklist
, it is considered a multipath device, and
SYSTEMD_READY=0
is set for it.
Later in the boot process, the system attempts to mount additional file
systems like /var
and /home
.
Usually, these file systems will be on the same device as the root file
system, by default as BTRFS subvolumes of the root file system itself. But
systemd cannot mount them because of SYSTEMD_READY=0
.
We are in a deadlock: The dm-multipath device cannot
be created, and the underlying device is blocked for systemd. The
additional file systems cannot be mounted, resulting in boot failure.
A solution to this problem already
exists. multipathd
detects this situation
and releases the device to systemd
which can then
proceed mounting the file system. However, it is important to understand
the general problem, which can still occur in more subtle ways.
18.15.2 Understanding device referencing issues #
An example of a device referencing issue has been given in
Section 18.7.4.2, “Persistent device names in the initramfs”. Typically, there are
multiple symbolic links pointing to a device node (see
Section 18.12.4, “Referring to multipath maps”). But these links do not always
exist; udev
creates them according to the current udev
rules. For example, if multipathing is off, symbolic links under
/dev/mapper/
for multipath devices will be missing.
Thus, any reference to a /dev/mapper/
device will
fail.
Such references can appear in various places, notably in
/etc/fstab
and /etc/crypttab
, in
the initramfs, or even on the kernel command line.
The safest way to circumvent this problem is to avoid using the kind of
device references that are not persistent between boots or depend on system
configuration. We generally recommend referring to file systems (and
similar entities like swap space) by properties of the file system itself
(like UUID or label) rather than the containing device. If such references
are not available and device references are required, for example, in
/etc/crypttab
, the options should be evaluated
carefully. For example, in Section 18.12.4, “Referring to multipath maps”, the
best option might be the /dev/disk/by-id/wwn-
link
because it would also work with multipath=off
.
18.15.3 Troubleshooting steps in emergency mode #
As there are many error situations that differ in subtle ways, it is impossible to provide a step-by-step recovery guide. But with the background knowledge from the previous subsections, you should be able to figure out the problem if a system runs into emergency mode because of multipathing issues. Before you begin debugging, make sure you have checked the following questions:
Is the multipath service enabled?
Is the multipath dracut module included in the initramfs?
Is my root device configured as a multipath device? If not, is the root device properly excluded from multipath as described in Section 18.11.1, “The
blacklist
section inmultipath.conf
”, or are you relying on the absence of the multipath module in the initramfs (see Section 18.3.2.2, “Root file system on a local disk”)?Does the system enter emergency mode before or after switching to the real root file system?
If you are unsure with respect to the last question, here is a sample dracut emergency prompt as it would be printed before switching root:
Generating "/run/initramfs/rdsosreport.txt" Entering emergency mode. Exit the shell to continue. Type "journalctl" to view system logs. You might want to save "/run/initramfs/rdsosreport.txt" to a USB stick or /boot after mounting them and attach it to a bug report. Give root password for maintenance (or press Control-D to continue):
The mention of rdsosreport.txt
is a clear indication
that the system is still running from the initramfs. If you are still
uncertain, log in and check for the existence of the file
/etc/initrd-release
. This file exists only in an
initramfs environment.
If emergency mode is entered after switching root, the emergency prompt
looks similar, but rdsosreport.txt
is not mentioned:
Timed out waiting for device dev-disk-by\x2duuid-c4a...cfef77d.device. [DEPEND] Dependency failed for Local File Systems. [DEPEND] Dependency failed for Postfix Mail Transport Agent. Welcome to emergency shell Give root password for maintenance (or press Control-D to continue):
Try to figure out what failed by examining failed systemd units and the journal.
#
systemctl --failed#
journalctl -b -o short-monotonicWhen looking at the journal, determine the first failed unit. When you have found the first failure, examine the messages before and around that point in time very carefully. Are there any warnings or other suspicious messages?
Watch out for the root switch ("
Switching root.
") and for messages about SCSI devices, device mapper, multipath, and LVM2. Look forsystemd
messages about devices and file systems ("Found device
…", "Mounting
…", "Mounted
…").Examine the existing devices, both low-level devices and device mapper devices (note that some of the commands below may not be available in the initramfs):
#
cat /proc/partitions#
ls -l /sys/class/block#
ls -l /dev/disk/by-id/* /dev/mapper/*#
dmsetup ls --tree#
lsblk#
lsscsiFrom the output of the commands above, you should get an idea whether the low-level devices were successfully probed, and whether any multipath maps and multipath partitions were set up.
If the device mapper multipath setup is not as you expect, examine the udev properties, in particular,
SYSTEMD_READY
(see above)#
udevadm info -eIf the previous step showed unexpected udev properties, something may have gone wrong during udev rule processing. Check other properties, in particular, those used for device identification (see Section 18.12.1, “WWIDs and device Identification”). If the udev properties are correct, check the journal for
multipathd
messages again. Look for "Device or resource busy
" messages.If the system failed to mount or otherwise activate a device, it is often helpful to try activating this device manually:
#
mount /var#
swapon -a#
vgchange -a yMostly, the manual activation will succeed and allow to proceed with system boot (usually by simply logging out from the emergency shell) and examine the situation further in the booted system.
If manual activation fails, you will probably see error messages that provide clues about what is going wrong. You can also try the commands again with increased verbosity.
At this point, you should have some idea what went wrong (if not, contact SUSE support and be prepared to answer most of the questions raised above).
You should be able to correct the situation with a few shell commands, exit the emergency shell, and boot successfully. You will still need to adjust your configuration to make sure the same problem will not occur again in the future.
Otherwise, you will need to boot the rescue system, set up the devices manually to
chroot
into the real root file system, and attempt to fix the problem based on the insight you got in the previous steps. Be aware that in this situation, the storage stack for the root file system may differ from normal. Depending on your setup, you may have force addition or omission of dracut modules when building a new initramfs. See also Section 18.7.4.1, “Enabling or disabling multipathing in the initramfs”.If the problem occurs frequently or even on every boot attempt, try booting with increased verbosity in order to get more information about the failure. The following kernel parameters, or a combination of them, are often helpful:
udev.log-priority=debug1 systemd.log_level=debug2 scsi_mod.scsi_logging_level=0204003 rd.debug4
In addition, it may make sense to enable logging for certain drivers and configure a serial console to capture the output during boot.
18.15.4 Technical Information Documents #
For more information about troubleshooting multipath I/O issues on SUSE Linux Enterprise Server, see the following Technical Information Documents (TIDs) in the SUSE Knowledgebase:
19 Managing Access Control Lists over NFSv4 #
There is no single standard for Access Control Lists (ACLs) in Linux beyond
the simple read, write, and execute (rwx
) flags for user,
group, and others (ugo
). One option for finer control is
the Draft POSIX ACLs, which were never formally
standardized by POSIX. Another is the NFSv4 ACLs, which were designed to be
part of the NFSv4 network file system with the goal of making something that
provided reasonable compatibility between POSIX systems on Linux and WIN32
systems on Microsoft Windows.
NFSv4 ACLs are not sufficient to correctly implement Draft POSIX ACLs so no
attempt has been made to map ACL accesses on an NFSv4 client (such as using
setfacl
).
When using NFSv4, Draft POSIX ACLs cannot be used even in emulation and NFSv4
ACLs need to be used directly; that means while setfacl
can work on NFSv3, it cannot work on NFSv4. To allow NFSv4 ACLs to be used on
an NFSv4 file system, SUSE Linux Enterprise Server provides the
nfs4-acl-tools
package, which contains the following:
nfs4-getfacl
nfs4-setfacl
nfs4-editacl
These operate in a generally similar way to getfacl
and
setfacl
for examining and modifying NFSv4 ACLs. These
commands are effective only if the file system on the NFS server provides
full support for NFSv4 ACLs. Any limitation imposed by the server will affect
programs running on the client in that some particular combinations of Access
Control Entries (ACEs) might not be possible.
It is not supported to mount NFS volumes locally on the exporting NFS server.
Additional Information#
For information, see Introduction to NFSv4 ACLs at http://wiki.linux-nfs.org/wiki/index.php/ACLs#Introduction_to_NFSv4_ACLs.
A GNU licenses #
This appendix contains the GNU Free Documentation License version 1.2.
GNU Free Documentation License #
Copyright (C) 2000, 2001, 2002 Free Software Foundation, Inc. 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.
0. PREAMBLE #
The purpose of this License is to make a manual, textbook, or other functional and useful document "free" in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or non-commercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others.
This License is a kind of "copyleft", which means that derivative works of the document must themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software.
We have designed this License to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference.
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4. MODIFICATIONS #
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5. COMBINING DOCUMENTS #
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In the combination, you must combine any sections Entitled "History" in the various original documents, forming one section Entitled "History"; likewise combine any sections Entitled "Acknowledgements", and any sections Entitled "Dedications". You must delete all sections Entitled "Endorsements".
6. COLLECTIONS OF DOCUMENTS #
You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects.
You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document.
7. AGGREGATION WITH INDEPENDENT WORKS #
A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, is called an "aggregate" if the copyright resulting from the compilation is not used to limit the legal rights of the compilation's users beyond what the individual works permit. When the Document is included in an aggregate, this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document.
If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document's Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form. Otherwise they must appear on printed covers that bracket the whole aggregate.
8. TRANSLATION #
Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail.
If a section in the Document is Entitled "Acknowledgements", "Dedications", or "History", the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title.
9. TERMINATION #
You may not copy, modify, sublicense, or distribute the Document except as expressly provided for under this License. Any other attempt to copy, modify, sublicense or distribute the Document is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance.
10. FUTURE REVISIONS OF THIS LICENSE #
The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See https://www.gnu.org/copyleft/.
Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License "or any later version" applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation.
ADDENDUM: How to use this License for your documents #
Copyright (c) YEAR YOUR NAME. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled “GNU Free Documentation License”.
If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with...Texts.” line with this:
with the Invariant Sections being LIST THEIR TITLES, with the Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST.
If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.
If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.