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SUSE Enterprise Storage 6, Ampere eMAG

SUSE® Enterprise Storage on Ampere® eMAG

Reference Architecture

The objective of this document is to present a step-by-step guide on how to implement SUSE Enterprise Storage® (6) on the Ampere® eMAG platform. It is suggested that the document be read in its entirety, along with the supplemental appendix information before attempting the process.

Author: Bryan Gartner, Senior Technology Strategist, SUSE
Publication Date: 2020-07-27

1 Introduction

The objective of this guide is to present a step-by-step guide on how to implement SUSE Enterprise Storage (6) on the Ampere eMAG platform. It is suggested that the document be read in its entirety, along with the supplemental appendix information before attempting the process.

The deployment presented in this guide aligns with architectural best practices and will support the implementation of all currently supported protocols as identified in the SUSE Enterprise Storage documentation.

Upon completion of the steps in this document, a working SUSE Enterprise Storage (6) cluster will be operational as described in the SUSE Enterprise Storage Deployment Guide.

2 Target Audience

This reference guide is targeted at administrators who deploy software defined storage solutions within their data centers and make that storage available to end users. By following this document, as well as those referenced herein, the administrator should have a full view of the SUSE Enterprise Storage architecture, deployment and administrative tasks, with a specific set of recommendations for deployment of the hardware and networking platform.

3 Business Value

SUSE Enterprise Storage

SUSE Enterprise Storage delivers a highly scalable, resilient, self-healing storage system designed for large scale environments ranging from hundreds of Terabytes to Petabytes. This software defined storage product can reduce IT costs by leveraging industry standard servers to present unified storage servicing block, file, and object protocols. Having storage that can meet the current needs and requirements of the data center while supporting topologies and protocols demanded by new web-scale applications, enables administrators to support the ever-increasing storage requirements of the enterprise with ease.

Ampere eMAG

The Ampere eMAG server is an high performance, power efficient data center class platform featuring 32 Ampere-designed 64-bit Armv8 cores running up to 3.3 GHz. Designed for cloud data center workloads, the eMAG server is ideal scalable performance applications like the SUSE Enterprise Storage stack. The server processor has the following features:

  • 32 Ampere Armv8 64-bit CPU cores at 3.3 GHz Sustained - SBSA Level 3

  • 32 KB L1 I-cache, 32KB L1 D-cache per core

  • Shared 256 KB L2 cache per 2 cores

  • 32MB globally shared L3 cache

  • 8x 72-bit DDR4-2667 channels

  • ECC, ChipKill, and DDR4 RAS features

  • Up to 16 DIMMs and 1TB/socket

  • 42 lanes of PCIE Gen 3, with 8 controllers

  • TDP: 75-125W

Also included in this configuration are the following key peripherals and infrastructure components that can be used to build a very high performance Ceph based storage cluster:

Micron

Enterprise IT and cloud managers want the fast, low latency and consistent performance of NVMe storage that won’t break the budget.

  • The 7300 NVMe SSDs leverage the low power consumption and price-performance efficiencies of 3D NAND technology and deliver fast NVMe IOPS and GB/s for a wide array of workloads.

  • Built with the innovative 96-layer 3D TLC NAND, the 5300 series combines the latest in NAND technology and a proven architecture to provide performance upgrades now and a path forward for moving to an all-flash future. The 5300’s high capacity, added security, and enhanced endurance enable strong performance.

NVIDIA

System Network Interface Card

MCX653105A-HDAT ConnectX-6 VPI Adapter is the world’s first 200Gb/s capable HDR InfiniBand and Ethernet network adapter card, offering industry-leading performance, smart offloads and in-network computing, leading to the highest return on investment for high-performance computing, cloud, web 2.0, storage and machine learning applications.

Network Switch

Spectrum-2 MSN3700C is a 1U 32-port 100GbE spine that can also be used as a high density 10/25GbE leaf when used with splitter cables. SN3700C allows for maximum flexibility, with ports spanning from 1GbE to 100GbE and port density that enables full rack connectivity to any server at any speed, and a variety of blocking ratios. SN3700C ports are fully splittable to up to 128 x 10/25GbE ports.

Broadcom

The high-port 9500-16i Tri-Mode, PCIe Gen 4.0 HBA is ideal for increased connectivity and maximum performance for enterprise data center flexibility. With increased bandwidth and IOPS performance compared to previous generations, the 9500-16i adapter delivers the performance and scalability needed by critical applications.

  • Connects up to 1024 SAS/SATA devices or 32 NVMe devices

  • Provides maximum connectivity and performance for high-end servers and applications

  • Support critical applications with the bandwidth of PCIe® 4.0 connectivity

  • Universal Bay Management (UBM) Ready

4 Hardware & Software

The recommended architecture for SUSE Enterprise Storage on Ampere eMAG leverages two models of Ampere servers. The role and functionality of each type of system within the SUSE Enterprise Storage environment will be explained in more detail in the architectural overview section.

Storage Nodes:
  • Ampere eMAG Core 2U Servers ( Lenovo HR350A )

Admin, monitor, and protocol gateways:
  • Ampere eMAG 32 Core 1U Servers ( Lenovo HR330A )

Switches:
  • NVIDIA Spectrum-2 MSN3700C 100Gb

Software:
  • SUSE Enterprise Storage (6)

  • SUSE Linux Enterprise Server 15 SP1

    TIP

    Please note that limited use SUSE Linux Enterprise Server operating system subscriptions are provided with SUSE Enterprise Storage as part of the subscription entitlement

5 Requirements

Enterprise storage systems require reliability, manageability, and serviceability. The legacy storage players have established a high threshold for each of these areas and now expect the software defined storage solutions to offer the same. Focusing on these areas helps SUSE make open source technology enterprise consumable. When combined with highly reliable and manageable hardware from Ampere, the result is a solution that meets the customer’s expectation.

5.1 Functional Requirements

A SUSE Enterprise Storage solution is:

  • Simple to setup and deploy, within the documented guidelines of system hardware, networking and environmental prerequisites.

  • Adaptable to the physical and logical constraints needed by the business, both initially and as needed over time for performance, security, and scalability concerns.

  • Resilient to changes in physical infrastructure components, caused by failure or required maintenance.

  • Capable of providing optimized object and block services to client access nodes, either directly or through gateway services.

6 Architectural Overview

This architecture overview section complements the SUSE Enterprise Storage Technical Overview document available online which presents the concepts behind software defined storage and Ceph as well as a quick start guide (non-platform specific).

6.1 Solution Architecture

SUSE Enterprise Storage provides unified block, file, and object access based on Ceph. Ceph is a distributed storage solution designed for scalability, reliability and performance. A critical component of Ceph is the RADOS object storage. RADOS enables a number of storage nodes to function together to store and retrieve data from the cluster using object storage techniques. The result is a storage solution that is abstracted from the hardware. Ceph supports both native and traditional client access. The native clients are aware of the storage topology and communicate directly with the storage daemons over the public network, resulting in horizontally scaling performance. Non-native protocols, such as ISCSI, S3, and NFS require the use of gateways. While these gateways may be thought of as a limiting factor, the ISCSI and S3 gateways can scale horizontally using load balancing techniques.

Ceph Architecture
Figure 1: Ceph Architecture

In addition to the required network infrastructure, the minimum SUSE Enterprise Storage cluster is comprised of a minimum of one administration server (physical or virtual), four object storage device nodes (OSDs), and three monitor nodes (MONs).

Specific to this implementation:
  • One system is deployed as the administrative host server. The administration host is the Salt-master and hosts the SUSE Enterprise Storage Administration Interface, openATTIC, which is the central management system which supports the cluster.

  • Three systems are deployed as monitor (MONs) nodes. Monitor nodes maintain information about the cluster health state, a map of the other monitor nodes and a CRUSH map. They also keep history of changes performed to the cluster.

  • Additional servers may be deployed as iSCSI gateway nodes. iSCSI is a storage area network (SAN) protocol that allows clients (called initiators) to send SCSI command to SCSI storage devices (targets) on remote servers. This protocol is utilized for block-based connectivity to environments such as Microsoft Windows, VMware, and traditional UNIX. These systems may be scaled horizontally through client usage of multi-path technology.

  • The RADOS gateway provides S3 and Swift based access methods to the cluster. These nodes are generally situated behind a load balancer infrastructure to provide redundancy and scalability. It is important to note that the load generated by the RADOS gateway can consume a significant amount of compute and memory resources making the minimum recommended configuration contain 6-8 CPU cores and 32GB of RAM.

  • SUSE Enterprise Storage requires a minimum of four systems as storage nodes. The storage nodes contain individual storage devices that are each assigned an Object Storage Daemon (OSD). The OSD assigned to the device stores data and manages the data replication and rebalancing processes. OSDs also communicate with the monitor (MON) nodes and provide them with the state of the other OSDs.

6.2 Networking Architecture

A software-defined solution is only as reliable as its slowest and least redundant component. This makes it important to design and implement a robust, high performance storage network infrastructure. From a network perspective for Ceph, this translates into:

  • Separation of cluster (backend) and client-facing (public) network traffic. This isolates Ceph OSD replication activities from Ceph clients. This may be achieved through separate physical networks or through use of VLANs.

  • Redundancy and capacity in the form of bonded network interfaces connected to switches.

The following figure shows the logical layout of the traditional Ceph cluster implementation.

Ceph Network Architecture
Figure 2: Ceph Network Architecture

7 Component Model

The preceding sections provided information on the both the overall Ampere hardware as well as an introduction to the Ceph software architecture. In this section, the focus is on the SUSE components: SUSE Linux Enterprise Server (SLES), SUSE Enterprise Storage (SES), and the Repository Mirroring Tool (RMT).

Component overview (SUSE)
  • SUSE Linux Enterprise Server - A world class secure, open source server operating system, equally adept at powering physical, virtual, or cloud-based mission-critical workloads. Service Pack 3 further raises the bar in helping organizations to accelerate innovation, enhance system reliability, meet tough security requirements and adapt to new technologies.

  • Repository Mirroring Tool (RMT) for SLES - allows enterprise customers to optimize the management of SUSE Linux Enterprise (and extensions such as SUSE Enterprise Storage) software updates and subscription entitlements. It establishes a proxy system for SUSE Customer Center (SCC) with repository and registration targets.

  • SUSE Enterprise Storage - Provided as an extension on top of SUSE Linux Enterprise Server, this intelligent software-defined storage solution, powered by Ceph technology with enterprise engineering and support from SUSE enables customers to transform enterprise infrastructure to reduce costs while providing unlimited scalability.

8 Deployment

This deployment section should be seen as a supplement online documentation. Specifically, the SUSE Enterprise Storage (6) Deployment Guide as well as SUSE Linux Enterprise Server Administration Guide. It is assumed that a Repository Mirroring Tool server exists within the environment. If not, please follow the information in Repository Mirroring Tool (RMT) for SLES to make one available. The emphasis is on specific design and configuration choices.

8.1 Network Deployment Overview

The following considerations for the network configuration should be attended to:

  • Ensure that all network switches are updated with consistent firmware versions.

  • Specific configuration for this deployment can be found in Appendix C: Network Switch Configuration & Appendix D: OS Networking Configuration

  • Network IP addressing and IP ranges need proper planning. In optimal environments, a single storage subnet should be used for all SUSE Enterprise Storage nodes on the primary network, with a separate, single subnet for the cluster network. Depending on the size of the installation, ranges larger than /24 may be required. When planning the network, current as well as future growth should be taken into consideration.

  • Setup DNS A records for all nodes. Decide on subnets and VLANs and configure the switch ports accordingly.

  • Ensure that you have access to a valid, reliable NTP service, as this is a critical requirement for all nodes. If not, it is recommended to use the admin node.

FunctionHostnamePrimary Network (VLAN)Cluster Network (VLAN)

Admin

amp-admin.suse.lab

172.16.227.60

N/A

Monitor

amp-mon1.suse.lab

172.16.227.61

N/A

Monitor

amp-mon2.suse.lab

172.16.227.62

N/A

Monitor

amp-mon3.suse.lab

172.16.227.63

N/A

Gateway

amp-gw1.suse.lab

172.16.227.64

N/A

Gateway

amp-gw2.suse.lab

172.16.227.65

N/A

OSD

amp-osd1.suse.lab

172.16.227.59

172.16.220.59

OSD

amp-osd2.suse.lab

172.16.227.58

172.16.220.58

OSD

amp-osd3.suse.lab

172.16.227.57

172.16.220.57

OSD

amp-osd4.suse.lab

172.16.227.56

172.16.220.56

OSD

amp-osd5.suse.lab

172.16.227.55

172.16.220.55

OSD

amp-osd6.suse.lab

172.16.227.54

172.16.220.54

OSD

amp-osd7.suse.lab

172.16.227.53

172.16.220.52

OSD

amp-osd8.suse.lab

172.16.227.52

172.16.220.52

OSD

amp-osd9.suse.lab

172.16.227.51

172.16.220.51

OSD

amp-osd10.suse.lab

172.16.227.50

172.16.220.50

8.2 Operating System Installation

There are several key tasks to ensure are performed correctly during the operating system installation.

  • During the SUSE Linux Enterprise installation, be sure and register the system with an update server. Ideally, this is a local RMT server which will reduce the time required for updates to be downloaded and applied to all nodes. By updating the nodes during installation, the system will deploy with the most up-to-date packages available, helping to ensure the best experience possible.

  • To speed installation, on the System Role screen, it is suggested to select Text Mode. The resulting installation is a text mode server that is an appropriate base OS for SUSE Linux Enterprise Server.

  • The next item is to ensure that the operating system is installed on the correct device. Especially on OSD nodes, the system may not choose the right drive by default. The proper way to ensure the right device is being used is to select Create Partition Setup on the Suggested Partitioning screen. This will then display a list of devices, allowing selection of the correct boot device. Next select Edit Proposal Settings and unselect the Propose Separate Home Partition checkbox.

  • Do ensure that NTP is configured to point to a valid, physical NTP server. This is critical for SUSE Enterprise Storage to function properly, and failure to do so can result in an unhealthy or non-functional cluster.

8.3 SUSE Enterprise Storage Installation & Configuration

8.3.1 Software Deployment configuration (Deepsea and Salt)

Salt, along with DeepSea, is a stack of components that help deploy and manage server infrastructure. It is very scalable, fast, and relatively easy to get running.

There are three key Salt imperatives that need to be followed:

  • The Salt Master is the host that controls the entire cluster deployment. Ceph itself should NOT be running on the master as all resources should be dedicated to Salt master services. In our scenario, we used the Admin host as the Salt master.

  • Salt minions are nodes controlled by Salt master. OSD, monitor, and gateway nodes are all Salt minions in this installation.

  • Salt minions need to correctly resolve the Salt master’s host name over the network. This can be achieved through configuring unique host names per interface (e.g. osd1-cluster.suse.lab and osd1-public.suse.lab) in DNS and/or local /etc/hosts files.

Deepsea consists of a series of Salt files to automate the deployment and management of a Ceph cluster. It consolidates the administrator’s decision making in a single location around cluster assignment, role assignment and profile assignment. Deepsea collects each set of tasks into a goal or stage.

The following steps, performed in order, will be used for this reference implementation:

  1. Install DeepSea on the Salt master which is the Admin node:

    zypper in deepsea
  2. Start the salt-master service and enable:

    systemctl start salt-master.service
    systemctl enable salt-master.service
  3. Install the salt-minion on all cluster nodes (including the Admin):

    zypper in salt-minion
  4. Configure all minions to connect to the Salt master:

    Modify the entry for master in the /etc/salt/minion

    master: sesadmin.domain.com
  5. Start the salt-minion service and enable:

    systemctl start salt-minion.service
    systemctl enable salt-minion.service
  6. List and accept all Salt keys on the Salt master: salt-key --accept-all and verify their acceptance:

    salt-key --list-all
    salt-key --accept-all
  7. Select the nodes to participate in the cluster:

    salt '*' grains.append deepsea default
  8. If the OSD nodes were used in a prior installation, zap ALL the OSD disks (ceph-disk zap <DISK>)

  9. At this point, the cluster can be deployed.

    1. Prepare the cluster:

      salt-run state.orch ceph.stage.prep
    2. Run the discover stage to collect data from all minions and create configuration fragments:

      salt-run state.orch ceph.stage.disovery
    3. A proposal for the storage layout needs to be generated at this time. For the hardware configuration used for this work, the following command was utilized:

      salt-run proposal.populate name=default target='amp-osd*'

      The result of the above command is a deployment proposal for the disks that places the RocksDB, Write-Ahead Log (WAL), and on the same device.

    4. A /srv/pillar/ceph/proposals/policy.cfg file needs to be created to instruct Salt on the location and configuration files to use for the different components that make up the Ceph cluster (Salt master, admin, monitor, and OSDs).

      • See Appendix B for the policy.cfg file used in the installation.

    5. Next, proceed with the configuration stage to parse the policy.cfg file and merge the included files into the final form

      salt-run state.orch ceph.stage.configure
    6. The last two steps manage the actual deployment.

      Deploy monitors and ODS daemons first:

      salt-run state.orch ceph.stage.deploy
      Note

      The command can take some time to complete, depending on the size of the cluster.

    7. Check for successful completion via:

      ceph -s
    8. Finally, deploy the services-gateways (iSCSI, RADOS, and openATTIC to name a few):

      salt-run state.orch ceph.stage.services

8.3.2 Post-deployment quick test

The steps below can be used (regardless of the deployment method) to validate the overall cluster health:

ceph status
ceph osd pool create test 1024
rados bench -p test 300 write --no-cleanup
rados bench -p test 300 seq

Once the tests are complete, you can remove the test pool via:

ceph tell mon.* injectargs --mon-allow-pool-delete=true
ceph osd pool delete test test --yes-i-really-really-mean-it
ceph tell mon.* injectargs --mon-allow-pool-delete=false

8.4 Deployment Considerations

Some final considerations before deploying your own version of a SUSE Enterprise Storage cluster, based on Ceph. As previously stated, please refer to the Administration and Deployment Guide.

  • With the default replication setting of 3, remember that the client-facing network will have about half or less of the traffic of the backend network. This is especially true when component failures occur or rebalancing happens on the OSD nodes. For this reason, it is important not to under provision this critical cluster and service resource.

  • It is important to maintain the minimum number of monitor nodes at three. As the cluster increases in size, it is best to increment in pairs, keeping the total number of Mon nodes as an odd number. However, only very large or very distributed clusters would likely need beyond the 3 MON nodes cited in this reference implementation. For performance reasons, it is recommended to use distinct nodes for the MON roles, so that the OSD nodes can be scaled as capacity requirements dictate.

  • As described in this implementation guide and the SUSE Enterprise Storage documentation, a minimum of four OSD nodes is recommended, with the default replication setting of 3. This will ensure cluster operation, even with the loss of a complete OSD node. Generally speaking, performance of the overall cluster increases as more properly configured OSD nodes are added.

9 Conclusion

The Ampere eMAG servers provides a strong capacity-oriented platform for enterprise, HPC or Cloud Ceph-based storage cluster. In addition to the strong raw performance demonstrated by this configuration as characterized in industry standard benchmarks like the IO500 workload, the Ampere systems provide a very compelling value proposition when combining its high performance the with the ultra-efficient power profile and the lighter than expected acquisition cost of the cluster! These features combined with the access flexibility and reliability of SUSE Enterprise Storage and industry leading support from Ampere allows any business to proceed confidently with a solution that addresses many storage use cases driven by the exponential growth in storage capacity and performance currently facing the industry.

10 Appendix A: Bill of Materials

RoleQtyComponentNotes

Admin, monitor, and protocol gateways

6

Ampere 1U Servers ( Lenovo HR330A )

Configuration:

  • 1x Ampere eMAG 8180 32Core 3.3GHz

  • 32GB DRAM ( 4x8 DIMM 2667 )

  • 2x Micron 7300 PRO NVMe M.2 480GB

  • 1x NVIDIA MCX653105A-HDAT ConnectX-6 VPI Adapter

OSD Nodes

10

Ampere 2U Servers ( Lenovo HR350A )

Configuration:

  • 1x Ampere eMAG 8180 32Core 3.3GHz

  • 128GB DRAM ( 8x16 DIMM 2667 )

  • 2x Micron 240GB NVMe M.2

  • 4x Micron 7300 PRO NVMe M.2 480GB

  • 1x Broadcom BRCM 9500-16i HBA

  • 1x NVIDIA MCX653105A-HDAT ConnectX-6 VPI Adapter

Network Switch

2

NVIDIA Spectrum-2 MSN3700C Switch

Updated with latest OS image

11 Appendix B: policy.cfg

cluster-ceph/cluster/*.sls
role-master/cluster/amp-admin*.sls
role-admin/cluster/amp-admin*.sls
role-mon/cluster/amp-mon*.sls
role-mgr/cluster/amp-mon*.sls
role-storage/cluster/amp-osd*.sls
role-mds/cluster/amp-[mo]*.sls
role-grafana/cluster/amp-admin*.sls
role-prometheus/cluster/amp-admin*.sls
config/stack/default/global.yml
config/stack/default/ceph/cluster.yml

12 Appendix C: Network Switch Configuration

The switch uplinks are configured with a LAG. The load generation nodes are blade servers connected with 16 10Gb ethernet ports bonded in two LACP bonds, one to each upstream switch. The cluster network carries back end and is VLAN 220.

##
## Active saved database "c3-mellanox-s3700"
## Generated at 2020/07/13 20:53:19 +0000
## Hostname: switch-6bdea0
## Product release: 3.9.0914
##

##
## Running-config temporary prefix mode setting
##
no cli default prefix-modes enable

##
## Interface Ethernet configuration
##
   interface port-channel 28
   interface port-channel 30
   fae interface ethernet 1/1 speed 100G no-autoneg
   fae interface ethernet 1/2 speed 100G no-autoneg
   fae interface ethernet 1/3 speed 100G no-autoneg
   fae interface ethernet 1/4 speed 100G no-autoneg
   fae interface ethernet 1/5 speed 100G no-autoneg
   fae interface ethernet 1/6 speed 100G no-autoneg
   fae interface ethernet 1/7 speed 100G no-autoneg
   fae interface ethernet 1/8 speed 100G no-autoneg
   fae interface ethernet 1/9 speed 100G no-autoneg
   fae interface ethernet 1/10 speed 100G no-autoneg
   fae interface ethernet 1/11 speed 100G no-autoneg
   fae interface ethernet 1/12 speed 100G no-autoneg
   fae interface ethernet 1/13 speed 100G no-autoneg
   fae interface ethernet 1/14 speed 100G no-autoneg
   fae interface ethernet 1/15 speed 100G no-autoneg
   fae interface ethernet 1/16 speed 100G no-autoneg
   fae interface ethernet 1/30 speed 100G no-autoneg
   interface ethernet 1/1-1/16 mtu 9216 force
   interface ethernet 1/28-1/30 mtu 9216 force
   interface port-channel 28 mtu 9216 force
   interface ethernet 1/1-1/16 switchport mode hybrid
   interface ethernet 1/28-1/29 channel-group 28 mode on
   interface ethernet 1/30-1/32 switchport mode hybrid
   interface port-channel 28 switchport mode hybrid
   interface port-channel 28 description uplink LACP

##
## LAG configuration
##
   lacp
   interface port-channel 28 lacp-individual enable force
   port-channel load-balance ethernet source-destination-mac

##
## VLAN configuration
##
   vlan 197
   vlan 220-2227
   interface ethernet 1/1-1/16 switchport access vlan 197
   interface ethernet 1/1-1/16 switchport hybrid allowed-vlan all
   interface ethernet 1/30-1/32 switchport hybrid allowed-vlan all
   interface port-channel 28 switchport hybrid allowed-vlan all
   vlan 197 name "pxe"
   vlan 220 name "storage"
   vlan 227 name "storage2"

13 Appendix D: OS Networking Configuration

Each host is configured with an active passive bond. This alleviates the need for switch based configuration to support the bonding and still provides sufficient bandwidth for all IO requests

/etc/sysconfig/network # cat ifcfg-eth0
BOOTPROTO='dhcp'
STARTMODE='auto'
#
/etc/sysconfig/network # cat ifcfg-vlan227
BOOTPROTO='static'
BROADCAST=''
ETHERDEVICE='eth0'
ETHTOOL_OPTIONS=''
IPADDR='172.16.227.50/24'
MTU=''
NAME=''
NETWORK=''
REMOTE_IPADDR=''
STARTMODE='auto'
VLAN_ID='227'
#
/etc/sysconfig/network # cat ifcfg-vlan220
BOOTPROTO='static'
BROADCAST=''
ETHERDEVICE='eth0'
ETHTOOL_OPTIONS=''
IPADDR='172.16.220.50/24'
MTU=''
NAME=''
NETWORK=''
REMOTE_IPADDR=''
STARTMODE='auto'
VLAN_ID='220'

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The "Title Page" means, for a printed book, the title page itself, plus such following pages as are needed to hold, legibly, the material this License requires to appear in the title page. For works in formats which do not have any title page as such, "Title Page" means the text near the most prominent appearance of the work’s title, preceding the beginning of the body of the text.

A section "Entitled XYZ" means a named subunit of the Document whose title either is precisely XYZ or contains XYZ in parentheses following text that translates XYZ in another language. (Here XYZ stands for a specific section name mentioned below, such as "Acknowledgements", "Dedications", "Endorsements", or "History".) To "Preserve the Title" of such a section when you modify the Document means that it remains a section "Entitled XYZ" according to this definition.

The Document may include Warranty Disclaimers next to the notice which states that this License applies to the Document. These Warranty Disclaimers are considered to be included by reference in this License, but only as regards disclaiming warranties: any other implication that these Warranty Disclaimers may have is void and has no effect on the meaning of this License.

2. VERBATIM COPYING

You may copy and distribute the Document in any medium, either commercially or noncommercially, provided that this License, the copyright notices, and the license notice saying this License applies to the Document are reproduced in all copies, and that you add no other conditions whatsoever to those of this License. You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute. However, you may accept compensation in exchange for copies. If you distribute a large enough number of copies you must also follow the conditions in section 3.

You may also lend copies, under the same conditions stated above, and you may publicly display copies.

3. COPYING IN QUANTITY

If you publish printed copies (or copies in media that commonly have printed covers) of the Document, numbering more than 100, and the Document’s license notice requires Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on the back cover. Both covers must also clearly and legibly identify you as the publisher of these copies. The front cover must present the full title with all words of the title equally prominent and visible. You may add other material on the covers in addition. Copying with changes limited to the covers, as long as they preserve the title of the Document and satisfy these conditions, can be treated as verbatim copying in other respects.

If the required texts for either cover are too voluminous to fit legibly, you should put the first ones listed (as many as fit reasonably) on the actual cover, and continue the rest onto adjacent pages.

If you publish or distribute Opaque copies of the Document numbering more than 100, you must either include a machine-readable Transparent copy along with each Opaque copy, or state in or with each Opaque copy a computer-network location from which the general network-using public has access to download using public-standard network protocols a complete Transparent copy of the Document, free of added material. If you use the latter option, you must take reasonably prudent steps, when you begin distribution of Opaque copies in quantity, to ensure that this Transparent copy will remain thus accessible at the stated location until at least one year after the last time you distribute an Opaque copy (directly or through your agents or retailers) of that edition to the public.

It is requested, but not required, that you contact the authors of the Document well before redistributing any large number of copies, to give them a chance to provide you with an updated version of the Document.

4. MODIFICATIONS

You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modified Version under precisely this License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it. In addition, you must do these things in the Modified Version:

  1. Use in the Title Page (and on the covers, if any) a title distinct from that of the Document, and from those of previous versions (which should, if there were any, be listed in the History section of the Document). You may use the same title as a previous version if the original publisher of that version gives permission.

  2. List on the Title Page, as authors, one or more persons or entities responsible for authorship of the modifications in the Modified Version, together with at least five of the principal authors of the Document (all of its principal authors, if it has fewer than five), unless they release you from this requirement.

  3. State on the Title page the name of the publisher of the Modified Version, as the publisher.

  4. Preserve all the copyright notices of the Document.

  5. Add an appropriate copyright notice for your modifications adjacent to the other copyright notices.

  6. Include, immediately after the copyright notices, a license notice giving the public permission to use the Modified Version under the terms of this License, in the form shown in the Addendum below.

  7. Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document’s license notice.

  8. Include an unaltered copy of this License.

  9. Preserve the section Entitled "History", Preserve its Title, and add to it an item stating at least the title, year, new authors, and publisher of the Modified Version as given on the Title Page. If there is no section Entitled "History" in the Document, create one stating the title, year, authors, and publisher of the Document as given on its Title Page, then add an item describing the Modified Version as stated in the previous sentence.

  10. Preserve the network location, if any, given in the Document for public access to a Transparent copy of the Document, and likewise the network locations given in the Document for previous versions it was based on. These may be placed in the "History" section. You may omit a network location for a work that was published at least four years before the Document itself, or if the original publisher of the version it refers to gives permission.

  11. For any section Entitled "Acknowledgements" or "Dedications", Preserve the Title of the section, and preserve in the section all the substance and tone of each of the contributor acknowledgements and/or dedications given therein.

  12. Preserve all the Invariant Sections of the Document, unaltered in their text and in their titles. Section numbers or the equivalent are not considered part of the section titles.

  13. Delete any section Entitled "Endorsements". Such a section may not be included in the Modified Version.

  14. Do not retitle any existing section to be Entitled "Endorsements" or to conflict in title with any Invariant Section.

  15. Preserve any Warranty Disclaimers.

If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document, you may at your option designate some or all of these sections as invariant. To do this, add their titles to the list of Invariant Sections in the Modified Version’s license notice. These titles must be distinct from any other section titles.

You may add a section Entitled "Endorsements", provided it contains nothing but endorsements of your Modified Version by various parties—​for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard.

You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher that added the old one.

The author(s) and publisher(s) of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version.

5. COMBINING DOCUMENTS

You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice, and that you preserve all their Warranty Disclaimers.

The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work.

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 http://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.

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