Quorum is a measure of cluster health and function that indicates how clusters address potential communications and connectivity issues. Quorum is maintained by a simple majority of nodes that are healthy and can communicate with each other. In a 4-node cluster, there is a possibility of a tie in the number of nodes that can communicate with each other. To avoid this, one node has an extra fractional voting weight called epsilon. Epsilon is a tie breaker that helps the cluster decide which node will maintain the master copy of the replicated databases (RDB). The node with epsilon will always be part of the quorum, unless it is unhealthy or isolated. References :- About quorum and epsilon, What is Cluster HA and how is Epsilon utilized to maintain RDB Quorum?