CMM Quorum

The Sun Cluster and Solstice HA clustering products determine CMM quorum by different methods. In previous Sun Cluster releases, including Sun Cluster 2.0 and 2.1, the cluster framework determined CMM quorum. In Solstice HA, quorum was determined by the volume manager, Solstice DiskSuite. Sun Cluster 2.2 is an integrated release based on both Sun Cluster 2.1 and Solstice HA 1.3. In Sun Cluster 2.2, determining CMM quorum depends on the volume manager (Solstice DiskSuite or VxVM). If Solstice DiskSuite is the volume manager, CMM quorum is determined by a quorum of metadevice state database replicas managed by Solstice DiskSuite. If VxVM is used as the volume manager, CMM quorum is determined by the cluster framework.

For Sun Cluster 2.2, CMM quorum is determined by the following:

• In clusters using VxVM, the cluster quorum is agreed upon based on the number of participating nodes, and another independent device. In two-node clusters, a quorum device provides a third vote toward quorum. In greater-than-two-node clusters, an exclusive lock mechanism, a nodelock, is used to decide quorum if the cluster becomes split.

• In clusters using Solstice DiskSuite, cluster quorum is agreed upon based on metadevice state database replicas or mediators. In configurations with at least three disk strings, the metadevice state database replicas can always determine whether a node is part of the cluster quorum. In two-node configurations with only two disk strings, the concept of a mediator was developed. Mediators work in a similar manner to the quorum device in VxVM. Refer to the chapter on mediators in the Sun Cluster 2.2 System Administration Guide for details.

It is necessary to determine cluster quorum when nodes join or leave the cluster and in the event that the cluster interconnect fails. In Solstice HA 1.3, cluster interconnect failure was considered a double failure and the software guaranteed to preserve data integrity, but did not guarantee that the cluster could continue without user intervention. Manual intervention for dual failures was part of the system design, as the safest method to ensure data integrity.

Sun Cluster 2.2 software attempts to preserve data integrity and also to maintain cluster availability without user intervention. To preserve cluster availability, Sun Cluster 2.2 implements several new processes. These include quorum devices and the Terminal Concentrator or System Service Processor. Note that just as Solstice HA 1.3 used Solstice DiskSuite to determine cluster quorum, Sun Cluster 2.2 also uses the volume manager as the primary factor in determining cluster quorum and cluster behavior upon failure of the cluster interconnect. The results of cluster interconnect failure are described in "Quorum Devices (VxVM)".