How to configure SBD in 2 node pacemaker cluster setup with qdevice .

Environment

• Red Hat Enterprise Linux Clustering
• Pacemaker
• RHEL 8

Issue

• Configuration of sbd auto-enabled auto_tie_breaker feature which makes the cluster unstable in case of a node failure .

Resolution

1. In a two node cluster setup, it is recommended to configure a quorum device before enabling sbd. This will avoid the enabling of auto_tie_breaker directive during the configuration of sbd.
2. Configure the SBD using the steps below :

# pcs stonith sbd enable 

3. If the server is configured to run a quorum device and the value of SBD_WATCHDOG_TIMEOUT in /etc/sysconfig/sbd is less than the value of qdevice sync_timeout, a quorum state update could be delayed for so long that it would result in a split-brain situation. If that happens, sbd could self-fence. Please verify this by following the resolution steps to set the qdevice's sync_timeout to be less than sbd_watchdog_timeout

4. Now, go ahead and stop/start the cluster and add a stonith-watchdog-timeout

# pcs cluster stop --all

# pcs cluster start --all

# pcs property set stonith-watchdog-timeout=15 

Root Cause

• When sbd is enabled in a cluster , auto_tie_breaker is enabled by default. When the auto_tie_breaker is used in even-number member clusters, then the failure of the partition containing the auto_tie_breaker_node (by default the node with lowest ID) will cause other partition to become inquorate and it will self-fence. In 2-node clusters with auto_tie_breaker this means that failure of node favored by auto_tie_breaker_node (typically nodeid 1) will result in reboot of other node (typically nodeid 2) that detects the inquorate state. If this is undesirable then corosync-qdevice can be used instead of the auto_tie_breaker to provide additional vote to quorum making behaviour closer to odd-number member clusters.

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