Spectrum Scale node quorum

Spectrum Scale 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 filesystem. This keeps any nodes that are cut off from the cluster (for example due to a network failure) from writing data to the filesystem. Maintaining quorum in a Spectrum Scale cluster means that a majority of the nodes designated as quorum nodes are able to successfully communicate.

Node quorum is the default quorum algorithm for Spectrum Scale. Node quorum is defined as one plus half of the explicitly defined quorum nodes in a cluster. This is considered as the node pool from which node quorum is derived.

There are no default quorum nodes. Nodes with a quorum role must be explicitly specified.

For the SUT: The SUT had four ECM nodes in total. A reasonable number of quorum nodes would be three. The general recommendation is to choose an odd number of quorum nodes. In a three node quorum configuration two nodes have to be communicating for cluster operations to continue.

Note: Another possibility would be a node quorum with tiebreaker disks. The cluster can remain online with only one surviving node. Typically tiebreaker disks are only used for two node clusters.

For more information on Spectrum Scale Quorum, proceed to the IBM Spectrum Scale documentation at the IBM Knowledge Center:

https://www.ibm.com/docs/en/storage-scale/4.2.0

Then, search for the topic Node Failure and select Quorum.