Fencing is an important cluster task. It isolates a computer's cluster node when the node misbehaves, in order to protect the shared cluster resources and prevent cluster disruption. Fencing should not be used in a two-node cluster configuration because the nodes may go on a killing spree and kill each other. To work around this issue, you should implement a Quorum disk, as explained in Chapter 8, Two-node Cluster Considerations on CentOS 6. If you do not configure fencing, a misbehaving computer cluster node can corrupt the cluster data. This is why it is necessary to exclude the problematic cluster node from cluster configuration immediately. The name of the daemon running all fencing actions is fenced.

STONITH is a fencing technique that stands for Shoot The Other Node In The Head. STONITH fences a failed cluster node by rebooting or turning it off.

The following fencing devices are most commonly used in cluster environments: