Computer clusters require 3 or more voting member systems to be stable.
A 2-node cluster can become unstable in certain circumstances without a third node or a disk or network share quorum member. This separate disk or network share acts as an independent cluster node for cluster quorum operations. Each cluster member will update records on a disk or share quorum folder which allows other quorum members to know the availability and health of each of the other members.
On clusters with an even number of cluster members are vulnerable to a condition known as “Split Brain” where half of the members lose contact with the other half. The best solution for this is to create a disk or share quorum member.
- A quorum disk must have a partition of at least 512 MB
- A network share must have at least 5 MB space available
When the cluster quorum is created, a directory will be created and populated with data.
To create the quorum, run the following cluster commands
#Create the quorum configuration
Set-ClusterQuorum –Cluster <cluster name> -NodeMajority
To create a disk quorum witness
Set-ClusterQuorum -NodeAndDiskMajority “Cluster Disk 2″
Note: the disk name under the Failover Cluster Manager should likely be changed to a more descriptive name other than Cluster Disk x. This can be done easily inside the Failover Cluster Manager.
Set-ClusterQuorum -NodeAndFileShareMajority “\\fileserver\fsw“
Note: This network share must be on a system other than the clustered system. A network share cannot reside on the same cluster as the file system is managed by the cluster and must be available when the cluster is down or booting.