HP Serviceguard manual Use of a Quorum Server as the Cluster Lock, Quorum Server Operation

Arbitration for Data Integrity in Serviceguard Clusters

Use of a Quorum Server as the Cluster Lock

Use of a Quorum Server as the Cluster Lock

A quorum server can be used in clusters of any size. The quorum server is an alternate form of cluster lock that uses a server program running on a separate system for tie-breaking rather than a lock disk. Should two equal sized groups of nodes (exactly 50% of the cluster in each group) become separated from each other, the quorum server allows one group to achieve quorum and form the cluster, while the other group is denied quorum and cannot start a cluster.

The quorum server process runs on a machine outside of the cluster for which it is providing quorum services. The quorum server listens to connection requests from the Serviceguard nodes on a known port. The server maintains a special area in memory for each cluster, and when a node obtains the cluster lock, this area is marked so that other nodes will recognize the lock as “taken.” The cluster will maintain this mark during an off-on power cycle of the quorum server.

The operation of the quorum server is shown in Figure 7. When there is a loss of communication between node 1 and node 2, the quorum server chooses one node (in this example, node 2) to continue running in the cluster. The other node halts.

Figure 7 Quorum Server Operation

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