Veritas Volume Manager 5.1 SP1 Administrator"s Guide (5900-1506, April 2011)

The CVM functionality of VxVM maintains global state information for each
volume. This enables VxVM to determine which volumes need to be recovered
when a node crashes. When a node leaves the cluster due to a crash or by some
other means that is not clean, VxVM determines which volumes may have writes
that have not completed and the master node resynchronizes these volumes. It
can use dirty region logging (DRL) or FastResync if these are active for any of the
volumes.
Clean node shutdown must be used after, or in conjunction with, a procedure to
halt all cluster applications. Depending on the characteristics of the clustered
application and its shutdown procedure, a successful shutdown can require a lot
of time (minutes to hours). For instance, many applications have the concept of
draining, where they accept no new work, but complete any work in progress
before exiting. This process can take a long time if, for example, a long-running
transaction is active.
When the VxVM shutdown procedure is invoked, it checks all volumes in all shared
disk groups on the node that is being shut down. The procedure then either
continues with the shutdown, or fails for one of the following reasons:
■ If all volumes in shared disk groups are closed, VxVM makes them unavailable
to applications. Because all nodes are informed that these volumes are closed
on the leaving node, no resynchronization is performed.
■ If any volume in a shared disk group is open, the shutdown operation in the
kernel waits until the volume is closed. There is no timeout checking in this
operation.
Once shutdown succeeds, the node has left the cluster. It is not possible to access
the shared volumes until the node joins the cluster again.
Since shutdown can be a lengthy process, other reconfiguration can take place
while shutdown is in progress. Normally, the shutdown attempt is suspended
until the other reconfiguration completes. However, if it is already too far
advanced, the shutdown may complete first.
Cluster shutdown
If all nodes leave a cluster, shared volumes must be recovered when the cluster
is next started if the last node did not leave cleanly, or if resynchronization from
previous nodes leaving uncleanly is incomplete. CVM automatically handles the
recovery and resynchronization tasks when a node joins the cluster.
447Administering cluster functionality (CVM)
CVM initialization and configuration