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How DRL works in a cluster environment

When one or more nodes in a cluster crash, DRL must handle the recovery of all volumes that were in use by those nodes when the crashes occurred. On initial cluster startup, all active maps are incorporated into the recovery map during the volume start operation.

Nodes that crash (that is, leave the cluster as dirty) are not allowed to rejoin the cluster until their DRL active maps have been incorporated into the recovery maps on all affected volumes. The recovery utilities compare a crashed node's active maps with the recovery map and make any necessary updates before the node can rejoin the cluster and resume I/O to the volume (which overwrites the active map). During this time, other nodes can continue to perform I/O.

VxVM tracks which nodes have crashed. If multiple node recoveries are underway in a cluster at a given time, their respective recoveries and recovery map updates can compete with each other. VxVM tracks changes in the state of DRL recovery and prevents I/O collisions.

The master node performs volatile tracking of DRL recovery map updates for each volume, and prevents multiple utilities from changing the recovery map simultaneously.