What is votequorum in a RHEL 7 High Availability cluster, and is it required?

Environment

• Red Hat Enterprise Linux (RHEL) 7 with the High Availability Add On
• corosync

Issue

• What is votequorum?
• How do I use votequorum?
• Can I use pacemaker without votequorum?

Resolution

votequorum is a plugin to corosync that handles the calculation and management of quorum in a High Availability cluster. In previous releases of RHEL High Availability, quorum was managed by cman while membership and communication was handled by openais or corosync, whereas in RHEL 7 those features from cman have been merged into votequorum and/or corosync. Red Hat does not support the usage of corosync or pacemaker without votequorum in RHEL 7.

votequorum is configured automatically when a cluster is created by pcs cluster setup or using the pcsd web interface. votequorum and its various settings are configured through the quorum stanza in /etc/corosync/corosync.conf:

quorum {
provider: corosync_votequorum
two_node: 1
}

votequorum offers a number of configurable options and several features and improvements over cman in how certain special cases are handled, including but not limited to:

• two_node: Allows for one node to maintain quorum after losing contact with the other in a two node cluster

• auto_tie_breaker: Enable half of the total nodes to remain quorate after losing contact with the other half, based on the partition with the lowest node ID

• last_man_standing: Allows for a single node to remain quorate beyond the typical minimum number of votes that would normally be required, which may be useful in larger clusters where there is a need to continue providing a basic level of service regardless of how many nodes have failed. Further configurable through last_man_standing_window

These settings and more are explained in further detail in the votequorum(5) manpage.

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