VERITAS Volume Manager 3.5 Administrator's Guide (September 2002)

Administering VxVM in Cluster Environments
260 VERITAS Volume Manager Administrator’s Guide
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 are responsible for allocating a new log of
sufficient size.
To increase the size of an existing DRL log so that it can accommodate maps for extra
nodes, use the vxplex -o rm dis command to detach and remove the log plex, and then
use the vxassist addlog command to recreate the log.
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 DRLactive mapshave beenincorporated intothe 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.
Administering VxVM in Cluster Environments
The following sections describe procedures for administering the cluster functionality of
VxVM.
Note Most VxVM commands require superuser or equivalent privileges.