How to ensure which failover cluster partition maintains quorum in a split scenario

How to ensure which failover cluster partition maintains quorum in a split scenario

Q. What can I do in Windows Server 2012 R2 to ensure a certain cluster partition wins in the event of a split?

A. Clustering is very resilient in Windows Server 2012 R2 that can keep the cluster running in almost all situations however in the event of a split in the cluster you may want to control which partition maintains quorum and keeps running services, i.e. your primary datacenter. This is easy in Windows Server 2016 with the new site-awareness however it is trickier in Windows Server 2012 R2.

One option is the LowerQuorumPriorityNodeID property which is configured on the cluster to specify a specific node that in the event of a 50-50 vote split should lose its vote thereby causing its partition to lose quorum and keep the other partition running. You would configure this node as one in the secondary location.

The challenge is the LowerQuorumPriorityNodeID only applies in a 50-50 split which often will not be the case as in Windows Server 2012 R2 you should always configure a witness resource which dynamically has its vote status changed depending on the number of nodes and ensures there is always an odd number of votes. What actually happens is the core cluster group is owned by a node in the cluster and that core cluster group includes the witness resource. In the event of a cluster split the partition that already owns the core cluster group and therefore the witness will typically keep it and therefore maintain quorum. This means you can proactively move the core cluster group to a node in your preferred site to help ensure that site would stay active. It can be moved using:

Move-ClusterGroup "cluster group" -Node <target node>

It can also be moved through Failover Cluster Manager via the More Actions - Move Core Cluster Resources context menu for the cluster.

Therefore make sure the core cluster group is running on your preferred site AND set the LowerQuorumPriorityNodeID to a node in the secondary site to try and ensure your primary site will win in the event of a split.

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