Use of Arbitrator Nodes

One way to ensure that split-brain situations do not arise is to devise an architecture that makes an even partition of the cluster impossible or at least extremely unlikely. A single failure in a four-node cluster could result in two equal-sized partitions, but a single failure in a five-node cluster could not. The fifth node in the cluster, then, performs the job of arbitration by virtue of the fact that it makes the number of nodes in the cluster odd. This type of node is sometimes called an arbitrator node, although it may be indistinguishable from other cluster nodes and is not configured in any special way in the cluster configuration file. This kind of arbitration is especially useful when nodes in the cluster are separated by significant distances, as in extended distance clusters or metropolitan clusters. Arbitrator nodes may be configured to run non-clustered applications, or they can be set up purely as arbitrators, with no other applications running other than Serviceguard.

The use of an arbitrator node is shown in Figure below. The single system in Data Center 3 is an arbitrator node.

Figure below: Use of Arbitrator Node

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