About persistent and replicated message queue

VCS includes a sophisticated mechanism for maintaining event messages, which ensures that messages are not lost. On each node, VCS queues messages to be sent to the notifier process. This queue is persistent as long as VCS is running and the contents of this queue remain the same on each node. If the notifier service group fails, notifier is failed over to another node in the cluster. Because the message queue is consistent across nodes, notifier can resume message delivery from where it left off even after failover.