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VCS service groups fall in three main categories: failover, parallel, and hybrid.
A failover service group runs on one system in the cluster at a time. Failover groups are used for most applications that do not support multiple systems to simultaneously access the application's data.
A parallel service group runs simultaneously on more than one system in the cluster. A parallel service group is more complex than a failover group. Parallel service groups are appropriate for applications that manage multiple application instances running simultaneously without data corruption.
A hybrid service group is for replicated data clusters and is a combination of the failover and parallel service groups. It behaves as a failover group within a system zone and a parallel group across system zones.
See About system zones.
A hybrid service group cannot fail over across system zones. VCS allows a switch operation on a hybrid group only if both systems are within the same system zone. If there are no systems within a zone for failover, VCS invokes the nofailover trigger on the lowest numbered node. Hybrid service groups adhere to the same rules governing group dependencies as do parallel groups.