This topic aims to explain the Quorum configuration in a Failover Clustering.
What’s a Failover Cluster Quorum
A Failover Cluster Quorum configuration specifies the number of failures that a cluster can support in order to keep working. Once the threshold limit is reached, the cluster stops working. The most common failures in a cluster are nodes that stop working or nodes that can’t communicate anymore.
Imagine that quorum doesn’t exist and you have two-nodes cluster. Now there is a network problem and the two nodes can’t communicate. If there is no Quorum, what prevents both nodes to operate independently and take disks ownership on each side? This situation is called Split-Brain. Quorum exists to avoid Split-Brain and prevents corruption on disks.
The Quorum is based on a voting algorithm. Each node in the cluster has a vote. The cluster keeps working while more than half of the voters are online. This is the quorum (or the majority of votes). When there are too many of failures and not enough online voters to constitute a quorum, the cluster stop working.