Arbitration For Data Integrity in Serviceguard Clusters, July 2007

Arbitration for Data Integrity in Serviceguard Clusters

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 8. The single system in

Data Center 3 is an arbitrator node.

Figure 8 Use of Arbitrator Node