SAP HANA System Replication Scale-Up - Performance Optimized Scenario #

For the SAPHanaSR-angi package configuration as decribed in this document, we limit the support to scale-up (single-box to single-box) system replication with the following configurations and parameters:

For the HA/DR provider hook scripts susHanaSR.py and susTkOver.py, the following requirements apply:

For the HA/DR provider hook script susChkSrv.py, the following requirements apply:

See also manual pages SAPHanaSR(7), susHanaSR.py(7), susTkOver.py(7) and susChkSrv.py(7) for more details and requirements.

Important

Without a valid STONITH method, the complete cluster is unsupported and will not work properly.

If you need to implement a different scenario, we strongly recommend to define a Proof of Concept (PoC) with SUSE. This PoC will focus on testing the existing solution in your scenario. Most of the above mentioned limitations are set because careful testing is needed.

This document describes how to set up the cluster to control SAP HANA in System Replication scenarios. The document focuses on the steps to integrate an already installed and working SAP HANA with System Replication. To create this document, SUSE Linux Enterprise Server for SAP Applications 15 SP6 was used. However, the concept can also be used with SUSE Linux Enterprise Server for SAP Applications 15 SP4 or newer.

The described example setup builds an SAP HANA HA cluster in two data centers in Walldorf (WDF) and in Rot (ROT), installed on two SLES for SAP 15 SP6 systems.

Figure 7: Cluster with SAP HANA SR - performance optimized #

 

You can either set up the cluster using the YaST wizard, doing it manually or using your own automation.

If you prefer to use the YaST wizard, you can use the shortcut yast sap_ha to start the module. The procedure to set up SAPHanaSR-angi using YaST is described in the product documentation of SUSE Linux Enterprise Server for SAP Applications in section Setting Up an SAP HANA Cluster at https://documentation.suse.com/sles-sap/15-SP6/html/SLES-SAP-guide/cha-cluster.html.

Figure 8: Scenario Selection for SAP HANA in the YaST Module sap_ha #

 

This guide focuses on the manual setup of the cluster to explain the details and to give you the possibility to create your own automation.

The seven main setup steps are:

Planning the installation is essential for a successful SAP HANA cluster setup.

Before you start, you need the following:

4.1 Minimum lab requirements and prerequisites #

 

Note

The minimum lab requirements mentioned here are by no means SAP sizing information. These data are provided only to rebuild the described cluster in a lab for test purposes. Even for tests the requirements can increase, depending on your test scenario. For productive systems ask your hardware vendor or use the official SAP sizing tools and services.

Note

Refer to SAP HANA TDI documentation for allowed storage configuration and file systems.

Requirements with 1 SAP system replication instance per site (1 : 1) - without a majority maker (2 node cluster):

• 2 VMs with each 32GB RAM, 50GB disk space for the system

• 1 shared disk for SBD with 10 MB disk space

• 2 data disks (one per site) with a capacity of each 96GB for SAP HANA

• 1 additional IP address for takeover

• 1 optional IP address for the read-enabled setup

• 1 optional IP address for HAWK Administration GUI

Requirements with 1 SAP instance per site (1 : 1) - with a majority maker (3 node cluster):

• 2 VMs with each 32GB RAM, 50GB disk space for the system

• 1 VM with 2GB RAM, 50GB disk space for the system

• 2 data disks (one per site) with a capacity of each 96GB for SAP HANA

• 1 additional IP address for takeover

• 1 optional IP address for the read-enabled setup

• 1 optional IP address for HAWK Administration GUI

This section contains information you should consider during the installation of the operating system.

For the scope of this document, first SUSE Linux Enterprise Server for SAP Applications is installed and configured. Then the SAP HANA database including the system replication is set up. Finally the automation with the cluster is set up and configured.

5.1 Installing SUSE Linux Enterprise Server for SAP Applications #

 

Multiple installation guides already exist, for different purposes and with different reasons to set up the server in a certain way. Below it is outlined where this information can be found. In addition, you will find important details you should consider to get a well-working system in place.

5.1.1 Installing the base operating system #

 

Depending on your infrastructure and the hardware used, you need to adapt the installation. All supported installation methods and minimum requirement are described in the Deployment Guide for SUSE Linux Enterprise Server (https://documentation.suse.com/sles/15-SP6/single-html/SLES-deployment/). In case of automated installations you can find further information in the AutoYaST Guide (https://documentation.suse.com/sles/15-SP6/html/SLES-all/book-autoyast.html). The main installation guides for SUSE Linux Enterprise Server for SAP Applications that fit all requirements for SAP HANA are available from the SAP notes:

• 2578899 SUSE Linux Enterprise Server 15: Installation Note

• 2684254 SAP HANA DB: Recommended OS settings for SLES 15 / SLES for SAP Applications 15

5.1.2 Installing additional software #

 

With SUSE Linux Enterprise Server for SAP Applications, SUSE delivers special resource agents for SAP HANA. With the pattern sap-hana, the old-style resource agent package SAPHanaSR is installed. This package needs to be replaced by the new SAPHanaSR-angi package. Follow the instructions below on each node if you have installed the systems based on SAP note 2578899. The pattern High Availability summarizes all tools recommended to be installed on all nodes, including the majority maker.

Example 1: Installing additional software for the HA cluster #

 

1. Install the High Availability pattern. Do this on all nodes.

   suse01:~ # zypper in --type pattern ha_sles

2. Uninstall the old-style package and install the new SAPHanaSR-angi resource agents. Do this on all nodes.

   suse01:~ # rpm -e --nodeps SAPHanaSR SAPHanaSR-doc
   suse01:~ # zypper in SAPHanaSR-angi

Note

Do not replace the package SAPHanaSR by SAPHanaSR-angi in an already running cluster. Upgrading from SAPHanaSR to SAPHanaSR-angi requires a specific procedure. See manual page SAPHanaSR_upgrade_to_angi(7) for details.

Installing the packages supportutils-plugin-ha-sap and ClusterTools2 is highly recommended. The first helps collecting data for support requests, the second simplifies common administrative tasks.

For more information, see section Installation and Setup of the SUSE Linux Enterprise High Availability Administration Guide.

Even though this document focuses on the integration of an installed SAP HANA with system replication already set up into the Linux cluster, this chapter summarizes the test environment. Always use the official documentation from SAP to install SAP HANA and to set up the system replication.

This guide shows SAP HANA and saphostagent with native systemd integration. An example for legacy SystemV is outlined in the appendix Section 12.5, “Example for checking legacy SystemV integration”.

# systemctl list-unit-files | grep sap
saphostagent.service enabled
sapinit.service generated
saprouter.service disabled
saptune.service enabled

# systemctl list-unit-files | grep SAP
SAPHA1_10.service enabled

# systemd-cgls -u SAP.slice
Unit SAP.slice (/SAP.slice):
├─saphostagent.service
│ ├─2630 /usr/sap/hostctrl/exe/saphostexec pf=/usr/sap/hostctrl/exe/host_profile -systemd
│ ├─2671 /usr/sap/hostctrl/exe/sapstartsrv pf=/usr/sap/hostctrl/exe/host_profile -D
│ └─3591 /usr/sap/hostctrl/exe/saposcol -l -w60 pf=/usr/sap/hostctrl/exe/host_profile
└─SAPHA1_10.service
  ├─ 1257 hdbcompileserver
  ├─ 1274 hdbpreprocessor
  ├─ 1353 hdbindexserver -port 31003
  ├─ 1356 hdbxsengine -port 31007
  ├─ 2077 hdbwebdispatcher
  ├─ 2300 hdbrsutil --start --port 31003 --volume 3 --volumesuffix mnt00001/hdb00003.00003 --identifier 1644426276
  ├─28462 /usr/sap/HA1/HDB10/exe/sapstartsrv pf=/usr/sap/HA1/SYS/profile/HA1_HDB10_suse01
  ├─31314 sapstart pf=/usr/sap/HA1/SYS/profile/HA1_HDB10_suse01
  ├─31372 /usr/sap/HA1/HDB10/suse01/trace/hdb.sapHA1_HDB10 -d -nw -f /usr/sap/HA1/HDB10/suse01/daemon.ini pf=/usr/sap/HA1/SYS/profile/HA1_HDB10_suse01
  ├─31479 hdbnameserver
  └─32201 hdbrsutil --start --port 31001 --volume 1 --volumesuffix mnt00001/hdb00001 --identifier 1644426203

For more information read the section Setting Up System Replication of the SAP HANA Administration Guide.

Procedure

7.1 Backing up the primary database #

 

Back up the primary database as described in the SAP HANA Administration Guide, section SAP HANA Database Backup and Recovery. We provide an example with SQL commands. You need to adapt these backup commands to match your backup infrastructure.

Example 2: Simple backup for the system database and all tenants with one single backup call #

 

As user <sid>adm enter the following command:

~> hdbsql -i 10 -u SYSTEM -d SYSTEMDB \
   "BACKUP DATA FOR FULL SYSTEM USING FILE ('backup')"

You will get a command output similar to the following:

0 rows affected (overall time 15.352069 sec; server time 15.347745 sec)

Example 3: Simple backup for a single container (non MDC) database #

 

Enter the following command as user <sid>adm:

~> hdbsql -i <instanceNumber> -u <dbuser> \
   "BACKUP DATA USING FILE ('backup')"

Important

Without a valid backup, you cannot bring SAP HANA into a system replication configuration.

7.2 Enabling the primary node #

 

As Linux user <sid>adm, enable the system replication at the primary node. You need to define a site name (like WDF). This site name must be unique for all SAP HANA databases which are connected via system replication. This means the secondary must have a different site name. The site names must not be changed later when the cluster has been activated.

Note

Do not use strings like "primary" and "secondary" as site names.

Example 4: Enable the Primary #

 

Enable the primary using the -sr_enable option.

suse01:~> hdbnsutil -sr_enable --name=WDF
checking local nameserver:
checking for active nameserver ...
nameserver is running, proceeding ...
configuring ini files ...
successfully enabled system as primary site ...
done.

Example 5: Check SR Configuration on the Primary #

 

Check the primary using the command hdbnsutil -sr_stateConfiguration.

suse01:~> hdbnsutil -sr_stateConfiguration --sapcontrol=1
SAPCONTROL-OK: <begin>
mode=primary
site id=1
site name=WDF
SAPCONTROL-OK: <end>
done.

The mode has changed from “none” to “primary”. The site now has a site name and a site ID.

suse02:~> HDB stop

~> cd /usr/sap/<SID>/SYS/global/security/rsecssfs
~> rsync -va {,<node1-siteB>:}$PWD/data/SSFS_<SID>.DAT
~> rsync -va {,<node1-siteB>:}$PWD/key/SSFS_<SID>.KEY

...
suse02:~> hdbnsutil -sr_register --name=ROT \
     --remoteHost=suse01 --remoteInstance=10 \
     --replicationMode=sync --operationMode=logreplay
adding site ...
checking for inactive nameserver ...
nameserver suse02:30001 not responding.
collecting information ...
updating local ini files ...
done.

suse02:~> HDB start
...
suse02:~> hdbnsutil -sr_stateConfiguration --sapcontrol=1
SAPCONTROL-OK: <begin>
mode=sync
site id=2
site name=ROT
active primary site=1
primary masters=suse01
SAPCONTROL-OK: <end>
done.

suse01:~> HDBSettings.sh systemReplicationStatus.py --sapcontrol=1
...
site/2/SITE_NAME=ROT
site/2/SOURCE_SITE_ID=1
site/2/REPLICATION_MODE=SYNC
site/2/REPLICATION_STATUS=ACTIVE
overall_replication_status=ACTIVE
site/1/REPLICATION_MODE=PRIMARY
site/1/SITE_NAME=WDF
local_site_id=1
...

This step is mandatory to inform the cluster immediately if the secondary gets out of sync. The hook is called by SAP HANA using the HA/DR provider interface in point-of-time when the secondary gets out of sync. This is typically the case when the first commit pending is released. The hook is called by SAP HANA again when the system replication is back. This HA/DR provider method is srConnectionChanged(), the related SUSE hook script is susHanaSR.py. The hook script susHanaSR.py is defacto mandatory.

Another hook is called by SAP HANA before an SR takeover is processed. This method can be used to block a manual takeover during normal cluster operation. This HA/DR provider method is preTakeover(), the related SUSE hook script is susTkOver.py.

A third hook is called by SAP HANA when a service status changes. This method can be used to speed up the takeover in case the indexserver process fails. This HA/DR provider method is srServiceStateChanged(), the related SUSE hook script is susChkSrv.py.

Procedure

This will implement three SAP HANA HA/DR provider hook scripts. The hook script susHanaSR.py does not need any configuration parameters. The configuration for susTkOver.py normally does not need to be adapted. The default for parameter sustkover_timeout is set to 30 seconds, which is good for most environments. The configuration shown for susChkSrv.py is a good starting point. Any tuning should be aligned with the SAP experts.

Note

All hook scripts should be used directly from the SAPHanaSR package. If the scripts are moved or copied, regular SUSE package updates will not work.

SAP HANA must be stopped to change the global.ini and allow SAP HANA to integrate the HA/DR hook scripts during start. Alternatively, SAPHanaSR-manageProvider might be used for adapting the global.ini. See manual page SAPHanaSR-manageProvider(8) for details.

~> sapcontrol -nr <instanceNumber> -function StopSystem

[ha_dr_provider_sushanasr]
provider = susHanaSR
path = /usr/share/SAPHanaSR-angi/
execution_order = 1

[trace]
ha_dr_sushanasr = info

ha1adm@suse02:/usr/sap/HA1/HDB10> sapcontrol -nr <instanceNumber> -function StopSystem

[ha_dr_provider_sustkover]
provider = susTkOver
path = /usr/share/SAPHanaSR-angi/
execution_order = 2

[trace]
ha_dr_sustkover = info
...

ha1adm@suse02:/usr/sap/HA1/HDB10> sapcontrol -nr <instanceNumber> -function StopSystem

[ha_dr_provider_suschksrv]
provider = susChkSrv
path = /usr/share/SAPHanaSR-angi/
execution_order = 3
action_on_lost=stop

[trace]
ha_dr_suschksrv = info
...

[system_replication]
operation_mode = logreplay

# SAPHanaSR-ScaleUp entries for writing srHook cluster attribute and SAPHanaSR-hookHelper
<sid>adm ALL=(ALL) NOPASSWD: /usr/sbin/crm_attribute -n hana_<sid>_*
<sid>adm ALL=(ALL) NOPASSWD: /usr/bin/SAPHanaSR-hookHelper --sid=<SID> *

# SAPHanaSR-ScaleUp entries for writing srHook cluster attribute
Cmnd_Alias SOK_SITEA    = /usr/sbin/crm_attribute -n hana_<sid>_site_srHook_<siteA> -v SOK   -t crm_config -s SAPHanaSR
Cmnd_Alias SFAIL_SITEA  = /usr/sbin/crm_attribute -n hana_<sid>_site_srHook_<siteA> -v SFAIL -t crm_config -s SAPHanaSR
Cmnd_Alias SOK_SITEB    = /usr/sbin/crm_attribute -n hana_<sid>_site_srHook_<siteB> -v SOK   -t crm_config -s SAPHanaSR
Cmnd_Alias SFAIL_SITEB  = /usr/sbin/crm_attribute -n hana_<sid>_site_srHook_<siteB> -v SFAIL -t crm_config -s SAPHanaSR
Cmnd_Alias HOOK_HELPER  = /usr/bin/SAPHanaSR-hookHelper --sid=<SID> --case=checkTakeover

<sid>adm ALL=(ALL) NOPASSWD: SOK_SITEA, SFAIL_SITEA, SOK_SITEB, SFAIL_SITEB, HOOK_HELPER

~> HDB start

~> cdtrace
~> grep HADR.*load.*susHanaSR nameserver_*.trc
~> grep susHanaSR.init nameserver_*.trc

~> cdtrace
~> grep HADR.*load.*susTkOver nameserver_*.trc
~> grep susTkOver.init nameserver_*.trc

~> cdtrace
~> grep HADR.*load.*susChkSrv nameserver_*.trc
~> grep susChkSrv.init nameserver_*.trc
~> egrep '(LOST:|STOP:|START:|DOWN:|init|load|fail)' nameserver_suschksrv.trc

~> cdtrace
~> grep susHanaSR.srConnection.*CRM nameserver_*.trc
~> grep susHanaSR.srConnection.*fallback nameserver_*.trc

# grep "sudo.*SAPHanaSR-hookHelper"  /var/log/messages

~> cdtrace
~> grep susTkOver.preTakeover.*permit nameserver_*.trc
~> grep susTkOver.preTakeover.*failed.*50277 nameserver_*.trc

This chapter describes the configuration of the cluster software SUSE Linux Enterprise High Availability, which is part of SUSE Linux Enterprise Server for SAP Applications, and the SAP HANA database integration.

9.1 Configuring the basic cluster #

 

The first step is to set up the basic cluster framework. For convenience, use YaST or the ha-cluster-init script. It is strongly recommended to add a second corosync ring, change it to UCAST communication and adjust the timeout values to fit your environment.

9.1.1 Setting up watchdog for "storage-based fencing" #

 

If you use the storage-based fencing (SBD) mechanism (diskless or disk-based), you must also configure a watchdog. The watchdog is needed to reset a node if the system cannot longer access the SBD (diskless or disk-based). It is mandatory to configure the Linux system for loading a watchdog driver. It is strongly recommended to use a watchdog with hardware assistance (as is available on most modern systems), such as hpwdt, iTCO_wdt, or others. As fallback, you can use the softdog module.

Example 18: Setup for Watchdog #

 

Important

Access to the watchdog timer: No other software must access the watchdog timer; it can only be accessed by one process at any time. Some hardware vendors ship systems management software that use the watchdog for system resets (for example HP ASR daemon). Such software must be disabled if the watchdog is to be used by SBD.

Determine the right watchdog module. Alternatively, you can find a list of installed drivers with your kernel version.

# ls -l /lib/modules/$(uname -r)/kernel/drivers/watchdog

Check if any watchdog module is already loaded.

# lsmod | egrep "(wd|dog|i6|iT|ibm)"

If you get a result, the system has already a loaded watchdog. If the watchdog does not match your watchdog device, you need to unload the module.

To safely unload the module, check first if an application is using the watchdog device.

# lsof /dev/watchdog
# rmmod <wrong_module>

Enable your watchdog module and make it persistent. For the example below, softdog has been used. However, softdog has some restrictions and should not be used as first option.

# echo softdog > /etc/modules-load.d/watchdog.conf
# systemctl restart systemd-modules-load

Check if the watchdog module is loaded correctly.

# lsmod | grep dog
# ls -l /dev/watchdog

Testing the watchdog can be done with a simple action. Ensure to switch of your SAP HANA first because the watchdog will force an unclean reset or shutdown of your system.

In case a hardware watchdog is used, a desired action is predefined after the timeout of the watchdog has reached. If your watchdog module is loaded and not controlled by any other application, do the following:

Important

Triggering the watchdog without continuously updating the watchdog resets/switches off the system. This is the intended mechanism. The following commands will force your system to be reset/switched off.

In case the softdog module is used, the following action can be performed:

# sync; cat /dev/watchdog & while date; do sleep 10; done

After your test was successful, you must implement the watchdog on all cluster members.

9.1.2 Setting up the initial cluster using ha-cluster-init #

 

For more detailed information about setting up a cluster, refer to the sections Setting Up the First Node and Adding the Second Node of the Installation and Setup Quick Start for SUSE Linux Enterprise High Availability 15 SP6 at https://documentation.suse.com/sle-ha/15-SP6/single-html/SLE-HA-installation/.

This setup uses unicast (UCAST) for corosync communication (-u option). Refer to the https://documentation.suse.com/sle-ha/15-SP6/single-html/SLE-HA-administration/ on detailed explanations of the terms unicast/multicast.

Create an initial setup, using the ha-cluster-init command, and follow the dialogs. Do this only on the first cluster node. Answer "no" to "Do you wish to configure a virtual IP address" and to "Do you want to configure QDevice".

To use two corosync rings make sure you have two interfaces configured and run:

suse01:~ # ha-cluster-init -u -M -s /dev/disk/by-id/SBDA -s /dev/disk/by-id/SBDB

To use only one corosync ring leave out the -M option (not recommended):

suse01:~ # ha-cluster-init -u -s /dev/disk/by-id/SBDA -s /dev/disk/by-id/SBDB

This command configures the basic cluster framework including:

• SSH keys

• csync2 to transfer configuration files

• SBD (two in this guide, better three for production)

• corosync (at least one ring, better two rings)

• HAWK Web interface

Important

As requested by ha-cluster-init, change the password of the user hacluster.

9.1.3 Checking and adapting the corosync and SBD configuration #

 

9.1.3.1 Checking the corosync configuration #

 

Check the following blocks in the file /etc/corosync/corosync.conf. The important parts are udpu and the correct ring/IP configuration.

See also the example at the end of this document and refer to the manual pages corosync.conf(5), votequorum(5) and corosync_overview(8) for details on parameters and features.

totem {
    ...

    interface {
        ringnumber: 0
        mcastport: 5405
        ttl: 1
    }

    interface {
        ringnumber: 1
        mcastport: 5407
        ttl: 1
    }

    rrp_mode: passive
    transport: udpu

    ...

}

    ...

nodelist {
    node {
            ring0_addr: 192.168.1.11
            ring1_addr: 192.168.2.11
            nodeid: 1
    }

    node {
            ring0_addr: 192.168.1.12
            ring1_addr: 192.168.2.12
            nodeid: 2
    }
}
    ...

9.1.3.2 Adapting the SBD configuration #

 

You can skip this section if you do not have any SBD devices, but be sure to implement another supported fencing mechanism.

See the manual pages sbd(8) and stonith_sbd(7) for details.

Table 3: SBD Options in File /etc/sysconfig/SBD #

 

Parameter	Description
SBD_WATCHDOG_DEV	Define the watchdog device. It is mandatory to use a watchdog. SBD does not work reliable without watchdog. Refer to the SLES manual and SUSE TID 7016880 for setting up a watchdog.
SBD_WATCHDOG_TIMEOUT	This parameter is used with diskless SBD. It defines the timeout, in seconds, the watchdog will wait before panicking the node if noone tickles it. If you set CIB parameter stonith-watchdog-timeout to a negative value, Pacemaker will automatically calculate this timeout and set it to twice the value of SBD_WATCHDOG_TIMEOUT starting with SUSE Linux Enterprise High Availability 15.
SBD_STARTMODE	Start mode. If set to clean, sbd will only start if the node was previously shut down cleanly or if the slot is empty.
SBD_PACEMAKER	Check Pacemaker quorum and node health.

In the following, replace /dev/disk/by-id/SBDA and /dev/disk/by-id/SBDB by your real sbd device names. As an example, the SBD_WATCHDOG_TIMEOUT is set to 20s to be less aggressive than the formerly used 5s.

# egrep -v "(^#|^$)" /etc/sysconfig/sbd
SBD_PACEMAKER=yes
SBD_STARTMODE="clean"
SBD_WATCHDOG_DEV="/dev/watchdog"
SBD_WATCHDOG_TIMEOUT="20"
SBD_TIMEOUT_ACTION="flush,reboot"
SBD_MOVE_TO_ROOT_CGROUP="auto"
SBD_OPTS=""
SBD_DEVICE="/dev/disk/by-id/SBDA;/dev/disk/by-id/SBDB"

Important

Also read the SUSE product documentation about calculation of timeouts for more details: https://documentation.suse.com/sle-ha/15-SP1/single-html/SLE-HA-guide/#sec-ha-storage-protect-watchdog-timings

9.1.3.3 Verifying the SBD device #

 

You can skip this section if you do not have any SBD devices, but make sure to implement a supported fencing mechanism.

It is a good practice to check if the SBD device can be accessed from both nodes and does contain valid records. Check this for all devices configured in /etc/sysconfig/sbd. You can do so, for example, by calling cs_show_sbd_devices.

suse01:~ # sbd -d /dev/disk/by-id/SBDA -d /dev/disk/by-id/SBDB dump
==Dumping header on disk /dev/disk/by-id/SBDA
Header version     : 2.1
UUID               : 0f4ea13e-fab8-4147-b9b2-3cdcfff07f86
Number of slots    : 255
Sector size        : 512
Timeout (watchdog) : 20
Timeout (allocate) : 2
Timeout (loop)     : 1
Timeout (msgwait)  : 40
==Header on disk /dev/disk/by-id/SBDA is dumped
==Dumping header on disk /dev/disk/by-id/SBDB
Header version     : 2.1
UUID               : 23c423df-675d-4937-a48c-5eb869fe0bb7
Number of slots    : 255
Sector size        : 512
Timeout (watchdog) : 20
Timeout (allocate) : 2
Timeout (loop)     : 1
Timeout (msgwait)  : 40
==Header on disk /dev/disk/by-id/SBDB is dumped

Important

The timeout values in our example are only start values. It is a requirement that they are tuned to your environment. Refer to the TIDs 7011346 and 7023689 for more information.

To check the current SBD entries for the various cluster nodes, you can use sbd list. If all entries are clear, no fencing task is marked in the SBD device.

suse01:~ # sbd -d /dev/disk/by-id/SBDA -d /dev/disk/by-id/SBDB list
0     suse01      clear
0     suse01      clear

For more information on SBD configuration parameters, consult the respective sections of the SUSE Linux Enterprise High Availability Administration Guide and the TIDs 7016880 and 7008216.

Now it is time to restart the cluster at the first node again (crm cluster start).

9.1.4 Configuring the cluster on the second node #

 

The second node of the two nodes cluster can be integrated by starting the command ha-cluster-join. This command asks for the IP address or name of the first cluster node. With this command, all needed configuration files are copied over. As a result, the cluster is started on both nodes.

# ha-cluster-join -c <host1>

Press RETURN to acknowledge the IP address.

9.1.5 Checking the cluster for the first time #

 

Now it is time to check and optionally start the cluster for the first time on both nodes.

suse01:~ # systemctl status pacemaker
suse01:~ # systemctl status sbd
suse02:~ # systemctl status pacemaker
suse02:~ # systemctl status sbd
suse01:~ # crm cluster start
suse02:~ # crm cluster start

Check the cluster status with crm_mon. We use the option "-r" to also see resources, which are configured but stopped.

# crm_mon -r1

The command will show the "empty" cluster and will print something similar to the screen output below. The most interesting pieces of information for now are that there are two nodes in the status "online", the message "partition with quorum", and a running SBD resource.

Cluster Summary:
  * Stack: corosync
  * Current DC: suse01 (version 2.0.5+20201202.ba59be712-150300.4.16.1-2.0.5+20201202.ba59be712) - partition with quorum
  * Last updated: Thu Jun 10 08:32:58 2022
  * Last change:  Thu Jun 10 08:29:41 2022 by hacluster via crmd on suse01
  * 2 nodes configured
  * 1 resource instance configured

Node List:
  * Online: [ suse01 suse02  ]

Full List of Resources:
  * stonith-sbd	(stonith:external/sbd):	 Started suse01

suse01:~ # vi crm-fileXX
suse01:~ # crm configure load update crm-fileXX

suse01:~ # vi crm-bs.txt
# enter the following to crm-bs.txt
property cib-bootstrap-options: \
    stonith-enabled="true" \
    stonith-action="reboot" \
    stonith-timeout="150" \
    priority-fencing-delay="30"
rsc_defaults rsc-options: \
    resource-stickiness="1000" \
    migration-threshold="5000"
op_defaults op-options: \
    timeout="600" \
    record-pending=true

suse01:~ # crm configure load update crm-bs.txt

# vi crm-sbd.txt
# enter the following to crm-sbd.txt
primitive stonith-sbd stonith:external/sbd \
    params pcmk_delay_max="15"

suse01:~ # crm configure load update crm-sbd.txt

# vi crm-saphanatop.txt
# enter the following to crm-saphanatop.txt
primitive rsc_SAPHanaTop_HA1_HDB10 ocf:suse:SAPHanaTopology \
    op start interval=0 timeout=600 \
    op stop interval=0 timeout=300 \
    op monitor interval=50 timeout=600 \
    params SID=HA1 InstanceNumber=10
clone cln_SAPHanaTop_HA1_HDB10 rsc_SAPHanaTop_HA1_HDB10 \
    meta clone-node-max=1 interleave=true

suse01:~ # crm configure load update crm-saphanatop.txt

# vi crm-saphanafil.txt
# enter the following to crm-saphanafil.txt
primitive rsc_SAPHanaFil_HA1_HDB10 ocf:suse:SAPHanaFilesystem \
    op start interval=0 timeout=10 \
    op stop interval=0 timeout=20 \
    op monitor interval=120 timeout=120 \
    params SID=HA1 InstanceNumber=10 ON_FAIL_ACTION="fence"
clone cln_SAPHanaFil_HA1_HDB10 rsc_SAPHanaFil_HA1_HDB10 \
    meta clone-node-max=1 interleave=true

suse01:~ # crm configure load update crm-saphanafil.txt

# vi crm-saphanacon.txt
# enter the following to crm-saphanacon.txt
primitive rsc_SAPHanaCon_HA1_HDB10 ocf:suse:SAPHanaController \
    op start interval=0 timeout=3600 \
    op stop interval=0 timeout=3600 \
    op promote interval=0 timeout=900 \
    op demote interval=0 timeout=320 \
    op monitor interval=60 role=Promoted timeout=700 \
    op monitor interval=61 role=Unpromoted timeout=700 \
    params SID=HA1 InstanceNumber=10 PREFER_SITE_TAKEOVER=true \
        DUPLICATE_PRIMARY_TIMEOUT=7200 AUTOMATED_REGISTER=false \
    meta priority=100
clone mst_SAPHanaCon_HA1_HDB10 rsc_SAPHanaCon_HA1_HDB10 \
    meta clone-node-max=1 promotable=true interleave=true maintenance=true

suse01:~ # crm configure load update crm-saphanacon.txt

# vi crm-vip.txt
# enter the following to crm-vip.txt

primitive rsc_ip_HA1_HDB10 ocf:heartbeat:IPaddr2 \
    op monitor interval=10 timeout=20 \
    params ip=192.168.1.20

suse01:~ # crm configure load update crm-vip.txt

# vi crm-cs.txt
# enter the following to crm-cs.txt
colocation col_saphana_ip_HA1_HDB10 2000: rsc_ip_HA1_HDB10:Started \
    mst_saphana_HA1_HDB10:Promoted
order ord_saphana_HA1_HDB10 Optional: cln_SAPHanaTop_HA1_HDB10 \
    mst_SAPHanaCon_HA1_HDB10

suse01:~ # crm configure load update crm-cs.txt

# crm resource refresh mst_SAPHanaCon_HA1_HDB10
# cs_wait_for_idle -s 5
# crm resource maintenance mst_SAPHanaCon_HA1_HDB10 off

# vi crm-re.txt
# enter the following to crm-re.txt

primitive rsc_ip_HA1_HDB10_readenabled ocf:heartbeat:IPaddr2 \
    op monitor interval=10 timeout=20 \
    params ip=192.168.1.21
colocation col_saphana_ip_HA1_HDB10_readenabled 2000: \
    rsc_ip_HA1_HDB10_readenabled:Started mst_SAPHanaCon_HA1_HDB10:Unpromoted

The lists of tests will be further enhanced in one of the next updates of this document.

As with any cluster testing is crucial. Make sure that all test cases derived from customer expectations are implemented and passed fully. Otherwise the project is likely to fail in production.

The test prerequisite, if not described differently, is always that both nodes are booted, normal members of the cluster and the HANA RDBMS is running. The system replication is in sync (SOK).

10.1 Test cases for semi-automation #

 

In the following test descriptions we assume PREFER_SITE_TAKEOVER="true" and AUTOMATED_REGISTER="false".

Note

The following tests are designed to be run in sequence and depend on the exit state of the preceding tests.

10.1.1 Test: Stop primary database on site A (node 1) #

 

Example 19: Test STOP_PRIMARY_SITE_A #

 

Component: #

 

• Primary Database

Description: #

 

• The primary SAP HANA database is stopped during normal cluster operation.

Test Procedure: #

 

1. Stop the primary SAP HANA database gracefully as <sid>adm.

   suse01:~> HDB stop

Recovery Procedure: #

 

1. Manually register the old primary (on node 1) with the new primary after takeover (on node 2) as <sid>adm.

   suse01:~> hdbnsutil -sr_register --remoteHost=suse02 --remoteInstance=10 \
             --replicationMode=sync --operationMode=logreplay \
             --name=WDF

2. Restart the SAP HANA database (now secondary) on node 1 as root.

   # crm resource refresh rsc_SAPHanaCon_HA1_HDB10 suse01

Expected: #

 

1. The cluster detects the stopped primary SAP HANA database (on node 1) and marks the resource failed.

2. The cluster promotes the secondary SAP HANA database (on node 2) to take over as primary.

3. The cluster migrates the IP address to the new primary (on node 2).

4. After some time the cluster shows the sync_state of the stopped primary (on node 1) as SFAIL.

5. Because AUTOMATED_REGISTER="false" the cluster does not restart the failed SAP HANA database or register it against the new primary.

6. After the manual register and resource refresh the system replication pair is marked as in sync (SOK).

7. The cluster "failed actions" are cleaned up after following the recovery procedure.

10.1.2 Test: Stop primary database on site B (node 2) #

 

Example 20: Test STOP_PRIMARY_DB_SITE_B #

 

Component:

Primary Database

Description:

The primary SAP HANA database is stopped during normal cluster operation.

Test Procedure: #

 

1. Stop the database gracefully as <sid>adm.

   suse02:~> HDB stop

Recovery Procedure: #

 

1. Manually register the old primary (on node 2) with the new primary after takeover (on node 1) as <sid>adm.

   suse02:~> hdbnsutil -sr_register --remoteHost=suse01 --remoteInstance=10 \
             --replicationMode=sync --operationMode=logreplay \
             --name=ROT

2. Restart the SAP HANA database (now secondary) on node 2 as root.

   # crm resource refresh rsc_SAPHanaCon_HA1_HDB10 suse02

Expected: #

 

1. The cluster detects the stopped primary SAP HANA database (on node 2) and marks the resource failed.

2. The cluster promotes the secondary SAP HANA database (on node 1) to take over as primary.

3. The cluster migrates the IP address to the new primary (on node 1).

4. After some time the cluster shows the sync_state of the stopped primary (on node 2) as SFAIL.

5. Because AUTOMATED_REGISTER="false" the cluster does not restart the failed SAP HANA database or register it against the new primary.

6. After the manual register and resource refresh the system replication pair is marked as in sync (SOK).

7. The cluster "failed actions" are cleaned up after following the recovery procedure.

10.1.3 Test: Crash primary database on site A (node 1) #

 

Example 21: Test CRASH_PRIMARY_DB_SITE_A #

 

Component:

Primary Database

Description:

Simulate a complete break-down of the primary database system.

Test Procedure: #

 

1. Kill the primary database system using signals as <sid>adm.

   suse01:~> HDB kill-9

Recovery Procedure: #

 

1. Manually register the old primary (on node 1) with the new primary after takeover (on node 2) as <sid>adm.

   suse01:~> hdbnsutil -sr_register --remoteHost=suse02 --remoteInstance=10 \
             --replicationMode=sync  --operationMode=logreplay \
             --name=WDF

2. Restart the SAP HANA database (now secondary) on node 1 as root.

   # crm resource refresh rsc_SAPHanaCon_HA1_HDB10 suse01

Expected: #

 

1. The cluster detects the stopped primary SAP HANA database (on node 1) and marks the resource failed.

2. The cluster promotes the secondary SAP HANA database (on node 2) to take over as primary.

3. The cluster migrates the IP address to the new primary (on node 2).

4. After some time the cluster shows the sync_state of the stopped primary (on node 1) as SFAIL.

5. Because AUTOMATED_REGISTER="false" the cluster does not restart the failed SAP HANA database or register it against the new primary.

6. After the manual register and resource refresh the system replication pair is marked as in sync (SOK).

7. The cluster "failed actions" are cleaned up after following the recovery procedure.

10.1.4 Test: Crash primary database on site B (node 2) #

 

Example 22: Test CRASH_PRIMARY_DB_SITE_B #

 

Component:

Primary Database

Description:

Simulate a complete break-down of the primary database system.

Test Procedure: #

 

1. Kill the primary database system using signals as <sid>adm.

   suse02:~> HDB kill-9

Recovery Procedure: #

 

1. Manually register the old primary (on node 2) with the new primary after takeover (on node 1) as <sid>adm.

   suse02:~> hdbnsutil -sr_register --remoteHost=suse01 --remoteInstance=10 \
             --replicationMode=sync  --operationMode=logreplay \
             --name=ROT

2. Restart the SAP HANA database (now secondary) on node 2 as root.

   # crm resource refresh rsc_SAPHanaCon_HA1_HDB10 suse02

Expected: #

 

1. The cluster detects the stopped primary SAP HANA database (on node 2) and marks the resource failed.

2. The cluster promotes the secondary SAP HANA database (on node 1) to take over as primary.

3. The cluster migrates the IP address to the new primary (on node 1).

4. After some time the cluster shows the sync_state of the stopped primary (on node 2) as SFAIL.

5. Because AUTOMATED_REGISTER="false" the cluster does not restart the failed SAP HANA database or register it against the new primary.

6. After the manual register and resource refresh the system replication pair is marked as in sync (SOK).

7. The cluster "failed actions" are cleaned up after following the recovery procedure.

10.1.5 Test: Crash primary node on site A (node 1) #

 

Example 23: Test CRASH_PRIMARY_NODE_SITE_A #

 

Component:

Cluster node of primary site

Description:

Simulate a crash of the primary site node running the primary SAP HANA database.

Test Procedure: #

 

1. Crash the primary node by sending a 'fast-reboot' system request.

   suse01:~ # sync; echo b > /proc/sysrq-trigger

Recovery Procedure: #

 

1. If SBD fencing is used, pacemaker will not automatically restart after being fenced. In this case clear the fencing flag on all SBD devices and subsequently start pacemaker.

   suse01:~ # sbd -d /dev/disk/by-id/SBDA message suse01 clear
   suse01:~ # sbd -d /dev/disk/by-id/SBDB message suse01 clear
   ...

2. Start the cluster framework

   suse01:~ # crm cluster start

3. Manually register the old primary (on node 1) with the new primary after takeover (on node 2) as <sid>adm.

   suse01:~> hdbnsutil -sr_register --remoteHost=suse02 --remoteInstance=10 \
             --replicationMode=sync  --operationMode=logreplay \
             --name=WDF

4. Restart the SAP HANA database (now secondary) on node 1 as root.

   # crm resource refresh rsc_SAPHanaCon_HA1_HDB10 suse01

Expected: #

 

1. The cluster detects the failed node (node 1) and declares it UNCLEAN and sets the secondary node (node 2) to status "partition with quorum".

2. The cluster fences the failed node (node 1).

3. The cluster declares the failed node (node 1) OFFLINE.

4. The cluster promotes the secondary SAP HANA database (on node 2) to take over as primary.

5. The cluster migrates the IP address to the new primary (on node 2).

6. After some time the cluster shows the sync_state of the stopped primary (on node 2) as SFAIL.

7. If SBD fencing is used, then the manual recovery procedure will be used to clear the fencing flag and restart pacemaker on the node.

8. Because AUTOMATED_REGISTER="false" the cluster does not restart the failed SAP HANA database or register it against the new primary.

9. After the manual register and resource refresh the system replication pair is marked as in sync (SOK).

10. The cluster "failed actions" are cleaned up after following the recovery procedure.

10.1.6 Test: Crash primary node on site B (node 2) #

 

Example 24: Test CRASH_PRIMARY_NODE_SITE_B #

 

Component:

Cluster node of secondary site

Description:

Simulate a crash of the secondary site node running the primary SAP HANA database.

Test Procedure: #

 

1. Crash the secondary node by sending a 'fast-reboot' system request.

   suse02:~ # sync; echo b > /proc/sysrq-trigger

Recovery Procedure: #

 

1. If SBD fencing is used, pacemaker will not automatically restart after being fenced. In this case clear the fencing flag on all SBD devices and subsequently start pacemaker.

   suse02:~ # sbd -d /dev/disk/by-id/SBDA message suse02 clear
   suse02:~ # sbd -d /dev/disk/by-id/SBDB message suse02 clear
   ...

2. Start the cluster Framework

   suse02:~ # crm cluster start

3. Manually register the old primary (on node 2) with the new primary after takeover (on node 1) as <sid>adm.

   suse02:~> hdbnsutil -sr_register --remoteHost=suse01 --remoteInstance=10 \
             --replicationMode=sync  --operationMode=logreplay \
             --name=ROT

4. Restart the SAP HANA database (now secondary) on node 2 as root.

   # crm resource refresh rsc_SAPHanaCon_HA1_HDB10 suse02

Expected: #

 

1. The cluster detects the failed secondary node (node 2) and declares it UNCLEAN and sets the primary node (node 1) to status "partition with quorum".

2. The cluster fences the failed secondary node (node 2).

3. The cluster declares the failed secondary node (node 2) OFFLINE.

4. The cluster promotes the secondary SAP HANA database (on node 1) to take over as primary.

5. The cluster migrates the IP address to the new primary (on node 1).

6. After some time the cluster shows the sync_state of the stopped secondary (on node 2) as SFAIL.

7. If SBD fencing is used, then the manual recovery procedure will be used to clear the fencing flag and restart pacemaker on the node.

8. Because AUTOMATED_REGISTER="false" the cluster does not restart the failed SAP HANA database or register it against the new primary.

9. After the manual register and resource refresh the system replication pair is marked as in sync (SOK).

10. The cluster "failed actions" are cleaned up after following the recovery procedure.

10.1.7 Test: Stop the secondary database on site B (node 2) #

 

Example 25: Test STOP_SECONDARY_DB_SITE_B #

 

Component:

Secondary SAP HANA database

Description:

The secondary SAP HANA database is stopped during normal cluster operation.

Test Procedure: #

 

1. Stop the secondary SAP HANA database gracefully as <sid>adm.

   suse02:~> HDB stop

Recovery Procedure: #

 

1. Refresh the failed resource status of the secondary SAP HANA database (on node 2) as root.

   # crm resource refresh rsc_SAPHanaCon_HA1_HDB10 suse02

Expected: #

 

1. The cluster detects the stopped secondary database (on node 2) and marks the resource failed.

2. The cluster detects the broken system replication and marks it as failed (SFAIL).

3. The cluster restarts the secondary SAP HANA database on the same node (node 2).

4. The cluster detects that the system replication is in sync again and marks it as ok (SOK).

5. The cluster "failed actions" are cleaned up after following the recovery procedure.

10.1.8 Test: Crash the secondary database on site B (node 2) #

 

Example 26: Test CRASH_SECONDARY_DB_SITE_B #

 

Component:

Secondary SAP HANA database

Description:

Simulate a complete break-down of the secondary database system.

Test Procedure: #

 

1. Kill the secondary database system using signals as <sid>adm.

   suse02:~> HDB kill-9

Recovery Procedure: #

 

1. Clean up the failed resource status of the secondary SAP HANA database (on node 2) as root.

   # crm resource refresh rsc_SAPHanaCon_HA1_HDB10 suse02

Expected: #

 

1. The cluster detects the stopped secondary database (on node 2) and marks the resource failed.

2. The cluster detects the broken system replication and marks it as failed (SFAIL).

3. The cluster restarts the secondary SAP HANA database on the same node (node 2).

4. The cluster detects that the system replication is in sync again and marks it as ok (SOK).

5. The cluster "failed actions" are cleaned up after following the recovery procedure.

10.1.9 Test: Crash the secondary node on site B (node2) #

 

Example 27: Test CRASH_SECONDARY_NODE_SITE_B #

 

Component:

Cluster node of secondary site

Description:

Simulate a crash of the secondary site node running the secondary SAP HANA database.

Test Procedure: #

 

1. Crash the secondary node by sending a 'fast-reboot' system request.

   suse02:~ # sync; echo b > /proc/sysrq-trigger

Recovery Procedure: #

 

1. If SBD fencing is used, pacemaker will not automatically restart after being fenced. In this case clear the fencing flag on all SBD devices and subsequently start pacemaker.

   suse02:~ # sbd -d /dev/disk/by-id/SBDA message suse02 clear
   suse02:~ # sbd -d /dev/disk/by-id/SBDB message suse02 clear
   ...

2. Start the cluster framework.

   suse02:~ # crm cluster start

Expected: #

 

1. The cluster detects the failed secondary node (node 2) and declares it UNCLEAN and sets the primary node (node 1) to status "partition with quorum".

2. The cluster fences the failed secondary node (node 2).

3. The cluster declares the failed secondary node (node 2) OFFLINE.

4. After some time the cluster shows the sync_state of the stopped secondary (on node 2) as SFAIL.

5. If SBD fencing is used, then the manual recovery procedure will be used to clear the fencing flag and restart pacemaker on the node.

6. When the fenced node (node 2) rejoins the cluster the former secondary SAP HANA database is started automatically.

7. The cluster detects that the system replication is in sync again and marks it as ok (SOK).

10.1.10 Test: Failure of replication LAN #

 

Example 28: Test FAIL_NETWORK_SR #

 

Component:

Replication LAN

Description:

Loss of replication LAN connectivity between the primary and secondary node.

Test Procedure: #

 

1. Break the connection between the cluster nodes on the replication LAN.

Recovery Procedure: #

 

1. Re-establish the connection between the cluster nodes on the replication LAN.

Expected: #

 

1. After some time the cluster shows the sync_state of the secondary (on node 2) as SFAIL.

2. The primary SAP HANA database (node 1) "HDBSettings.sh systemReplicationStatus.py" shows "CONNECTION TIMEOUT" and the secondary SAP HANA database (node 2) is not able to reach the primary database (node 1).

3. The primary SAP HANA database continues to operate as “normal”, but no system replication takes place and is therefore no longer a valid take over destination.

4. When the LAN connection is re-established, HDB automatically detects connectivity between the SAP HANA databases and restarts the system replication process

5. The cluster detects that the system replication is in sync again and marks it as ok (SOK).

10.2 Test cases for full automation #

 

In the following test descriptions we assume PREFER_SITE_TAKEOVER="true" and AUTOMATED_REGISTER="true".

Note

The following tests are designed to be run in sequence and depend on the exit state of the preceding tests.

10.2.1 Test: Stop the primary database on site A #

 

Example 29: Test STOP_PRIMARY_DB_SITE_A #

 

Component: #

 

• Primary Database

Description: #

 

• The primary SAP HANA database is stopped during normal cluster operation.

Test Procedure: #

 

• Stop the primary SAP HANA database gracefully as <sid>adm.

suse01:~> HDB stop

Recovery Procedure: #

 

1. Not needed, everything is automated

2. Refresh the cluster resources on node 1 as root.

# crm resource refresh rsc_SAPHanaCon_HA1_HDB10 suse01

Expected: #

 

1. The cluster detects the stopped primary SAP HANA database (on node 1) and marks the resource failed.

2. The cluster promotes the secondary SAP HANA database (on node 2) to take over as primary.

3. The cluster migrates the IP address to the new primary (on node 2).

4. After some time the cluster shows the sync_state of the stopped primary (on node 1) as SFAIL.

5. Because AUTOMATED_REGISTER="true" the cluster does restart the failed SAP HANA database and register it against the new primary.

6. After the automated register and resource refresh the system replication pair is marked as in sync (SOK).

7. The cluster "failed actions" are cleaned up after following the recovery procedure.

10.2.2 Test: Crash the primary node on site B (node 2) #

 

Example 30: Test CRASH_PRIMARY_NODE_SITE_B #

 

Component: #

 

• Cluster node of site B

Description: #

 

• Simulate a crash of the site B node running the primary SAP HANA database.

Test Procedure: #

 

• Crash the secondary node by sending a 'fast-reboot' system request.

suse02:~ # sync; echo b > /proc/sysrq-trigger

Recovery Procedure: #

 

• If SBD fencing is used, pacemaker will not automatically restart after being fenced. In this case clear the fencing flag on all SBD devices and subsequently start pacemaker.

suse02:~ # sbd -d /dev/disk/by-id/SBDA message suse02 clear
suse02:~ # sbd -d /dev/disk/by-id/SBDB message suse02 clear
...

• Start the cluster framework.

suse02:~ # crm cluster start

• Refresh the cluster resources on node 2 as root.

# crm resource refresh rsc_SAPHanaCon_HA1_HDB10 suse02

Expected: #

 

1. The cluster detects the failed primary node (node 2) and declares it UNCLEAN and sets the primary node (node 2) to status "partition with quorum".

2. The cluster fences the failed primary node (node 2).

3. The cluster declares the failed primary node (node 2) OFFLINE.

4. The cluster promotes the secondary SAP HANA database (on node 1) to take over as primary.

5. The cluster migrates the IP address to the new primary (on node 1).

6. After some time the cluster shows the sync_state of the stopped secondary (on node 2) as SFAIL.

7. If SBD fencing is used, then the manual recovery procedure will be used to clear the fencing flag and restart pacemaker on the node.

8. When the fenced node (node 2) rejoins the cluster the former primary became a secondary.

9. Because AUTOMATED_REGISTER="true" the cluster does restart the failed SAP HANA database and register it against the new primary.

10. The cluster detects that the system replication is in sync again and marks it as ok (SOK).

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The "Cover Texts" are certain short passages of text that are listed, as Front-Cover Texts or Back-Cover Texts, in the notice that says that the Document is released under this License. A Front-Cover Text may be at most 5 words, and a Back-Cover Text may be at most 25 words.

A "Transparent" copy of the Document means a machine-readable copy, represented in a format whose specification is available to the general public, that is suitable for revising the document straightforwardly with generic text editors or (for images composed of pixels) generic paint programs or (for drawings) some widely available drawing editor, and that is suitable for input to text formatters or for automatic translation to a variety of formats suitable for input to text formatters. A copy made in an otherwise Transparent file format whose markup, or absence of markup, has been arranged to thwart or discourage subsequent modification by readers is not Transparent. An image format is not Transparent if used for any substantial amount of text. A copy that is not "Transparent" is called "Opaque".

Examples of suitable formats for Transparent copies include plain ASCII without markup, Texinfo input format, LaTeX input format, SGML or XML using a publicly available DTD, and standard-conforming simple HTML, PostScript or PDF designed for human modification. Examples of transparent image formats include PNG, XCF and JPG. Opaque formats include proprietary formats that can be read and edited only by proprietary word processors, SGML or XML for which the DTD and/or processing tools are not generally available, and the machine-generated HTML, PostScript or PDF produced by some word processors for output purposes only.

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.

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.

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.

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:

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.

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".

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.

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.

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.

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.

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.

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.