STONITH is an acronym for Shoot-The-Other-Node-In-The-Head; its purpose is to protect your data from being corrupted by rogue nodes or concurrent access.

When a node is unresponsive it might still access your data. The only way to be 100% sure that your data is safe, is to use STONITH, so we can be certain that the node is truly offline, before allowing the data to be accessed from another node.

STONITH also has a role to play in the event that a clustered service cannot be stopped. In this case, the cluster uses STONITH to force the whole node offline, thereby making it safe to start the service elsewhere.