What purpose does a quorum device serve in SC3.0?

       Quorum devices increase availability of a cluster. In Sun Cluster 3.0, a quorum device is required in a 2-node cluster configuration to survive single points of failure in the cluster.

       Currently, we do not have disks that support SCSI-3 PGR, and this restricts the use of quorum devices to dual-ported quorum devices. These dual-ported or 2-ported quorum devices can be used to increase the availability of a cluster similar to their >2 ported counterparts. These dual-ported quorum devices can be used in various configs such as a 2-pair 4-node config or in an (N+1) 4-node config where each pair shares a quorum device. For example, in an (N+1) config, the cluster can survive the failure of N nodes provided the +1 node is up.