VERITAS Volume Manager 3.1 Administrator's Guide

Cluster Functionality
Dirty Region Logging and Cluster Environments
Chapter 7310
sufficient size.
How DRL Works in a Cluster Environment
When one or more nodes in a cluster crash, DRL needs to be able to
handle the recovery of all volumes in use by those nodes when the
crash(es) occurred. On initial cluster startup, all active maps are
incorporated into the recovery map during the volume start operation.
Nodes that crash (i.e., 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.
The VxVM kernel 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. The
VxVM kernel therefore tracks changes in the DRL recovery state and
prevents I/O operation collisions.
The master performs volatile tracking of DRL recovery map updates for
each volume and prevents multiple utilities from changing the recovery
map simultaneously.