Quorum is the name given to a mechanism which is intended to help solve the SplitBrain[1] problem, by selecting no more than one ClusterPartition[2] when failures in cluster communication cause the cluster to split into multiple ClusterPartition[2]s.
Once a ClusterPartition[2] is selected to have quorum, that partition can run services for the cluster.
The most well-known method of awarding quorum to a ClusterPartition[2] for an n-node cluster for quorum is to award quorum to that partition which has more than n/2 nodes in it.
Of course, this causes problems for the case where n is 2, since any failure at all will cause the entire cluster to shut down.
To aid in this problem, there are a variety of other methods available to compute quorum, or break ties in quorum voting.
In Linux-HA, we provide a QuorumDaemon[3] to help resolve this situation.
Split-brain, quorum, fencing overview[4], SplitBrain[1], fencing[5], QuorumDaemon[3]
| [1] | http://www.linux-ha.org/SplitBrain |
| [2] | http://www.linux-ha.org/ClusterPartition |
| [3] | http://www.linux-ha.org/QuorumDaemon |
| [4] | http://techthoughts.typepad.com/managing_computers/2007/10/split-brain-quo.html |
| [5] | http://www.linux-ha.org/fencing |
This information provided courtesy of the Linux-HA project at http://linux-ha.org/