Quorum

Quorum means "majority", and the idea behind quorum is easy to understand: if the Cluster doesn’t have quorum, no actions will be taken in the cluster. This by itself would offer a good solution to avoid the Split Brain problem.

But to make sure that it can never happen, that multiple nodes activate the same resources in the cluster, another mechanism is used as well. This mechanism is known as STONITH. (Van Vugt 2014, 6)

This is required to avoid corruption on vital Cluster resources, such as the File System.