Veritas Volume Manager 5.0.1 Administrator's Guide, HP-UX 11i v3, First Edition, November 2009

If a shared disk group is imported as a private disk group on a system without
cluster support, VxVM considers the logs of the shared volumes to be invalid and
conducts a full volume recovery. After the recovery completes, VxVM uses DRL.
The cluster functionality of VxVM can perform a DRL recovery on a non-shared
volume. However, if such a volume is moved to a VxVM system with cluster support
and imported as shared, the dirty region log is probably too small to accommodate
maps for all the cluster nodes. VxVM then marks the log invalid and performs a
full recovery anyway. Similarly, moving a DRL volume from a two-node cluster
to a four-node cluster can result in too small a log size, which the cluster
functionality of VxVM handles with a full volume recovery. In both cases, you
must allocate a new log of sufficient size.
See “Dirty region logging” on page 60.
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.
Multiple host failover configurations
Outside the context of clustering functionality, VxVM disk groups can be imported
(made available) from only one host at any given time. When a host imports a disk
group as private, the volumes and configuration of that disk group become
accessible to the host. If the administrator or system software wants to privately
use the same disk group from another host, the host that already has the disk
473Administering cluster functionality
Multiple host failover configurations