Quorum

GPFS™ uses a cluster mechanism called quorum to maintain data consistency in the event of a node failure.

Quorum operates on the principle of majority rule. This means that a majority of the nodes in the cluster must be successfully communicating before any node can mount and access a file system. This keeps any nodes that are cut off from the cluster (for example, by a network failure) from writing data to the file system.

During node failure situations, quorum needs to be maintained in order for the cluster to remain online. If quorum is not maintained due to node failure, GPFS unmounts local file systems on the remaining nodes and attempts to reestablish quorum, at which point file system recovery occurs. For this reason it is important that the set of quorum nodes be carefully considered (refer to Selecting quorum nodes for additional information).