9.3.4. Fencing and Network Partitions

A network partition is a a network failure that divides the cluster into two or more sub-clusters, where each broker can communicate with brokers in its own sub-cluster but not with brokers in other sub-clusters. This condition is also referred to as a "split brain".

Nodes in one sub-cluster can't tell whether nodes in other sub-clusters are dead or are still running but disconnected. We cannot allow each sub-cluster to independently declare its own qpidd primary and start serving clients, as the cluster will become inconsistent. We must ensure only one sub-cluster continues to provide service.

A quorum determines which sub-cluster continues to operate, and power fencing ensures that nodes in non-quorate sub-clusters cannot attempt to provide service inconsistently. For more information refer to the Red Hat Enterprise Linux 6 High Availability Add-on Overview Chapter 2. Quorum and Chapter 4. Fencing.