Each cluster has one assigned quorum resource •Used as a tie-breaker when nodes cannot communicate •Must be able to be arbitrated and controlled by one node •Able to store log data •Maintains cluster membership "accounts" •Handles changes to cluster configuration database
Quorum-capable resources: currently only disk resources are considered quorum capable.
Tie-breaker: when both nodes are running but not communicating, one node will gain control of the quorum resource. Since the quorum is capable of maintaining log data, the MSCS software can write any changes to the quorum resource.
Cluster membership: in order to form an active cluster, the first node up will gain control of the quorum resource. When the other node joins the cluster, ownership of the quorum resource can be traded. If one of the original nodes is replaced, the quorum will maintain the correct membership information.
Cluster configuration database: if some of the defined cluster members are down, then changes to the cluster configuration database are logged to this resource. No matter which node from the cluster fails, the cluster can always restore its latest state from the quorum resource. This process prevents the cluster from becoming partitioned (split-brain). Once the configuration changes have been processed by all defined cluster nodes, the change logs are flushed.
Because of the critical role that a quorum resource plays in the cluster, it is often composed of a RAID-1 array.
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