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Thursday, October 15, 2015

What is split-brain condition in Red Hat Cluster?

 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.