Answer»
- We say a cluster has quorum if a majority of nodes are alive, communicating, and agree on the active cluster members. For example, in a thirteen-NODE cluster, quorum is only REACHED if seven or more nodes are communicating. If the seventh node DIES, the cluster loses quorum and can no longer function.
- A cluster must maintain quorum to prevent split-brain ISSUES.
- If quorum was not enforced, quorum, a communication error on that same thirteen-node cluster may cause a situation where six nodes are operating on the shared storage, while another six nodes are also operating on it, independently. Because of the communication error, the two partial-clusters would overwrite areas of the disk and corrupt the file system.
- With quorum rules enforced, only ONE of the partial clusters can use the shared storage, thus protecting data integrity.
- Quorum doesn't prevent split-brain situations, but it does decide who is dominant and allowed to function in the cluster.
- quorum can be determined by a combination of communicating messages via Ethernet and through a quorum disk.
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