VERITAS Volume Manager 3.1 Administrator's Guide

Cluster Functionality
Cluster Functionality Overview
Chapter 7304
If a node attempts to join the cluster while a volume reconfiguration is
being performed, the results depend on how far the reconfiguration has
progressed. If the kernel is not yet involved, the volume reconfiguration
is suspended and restarted when the join is complete. If the kernel is
involved, the join waits until the reconfiguration is complete.
When an error occurs (such as when a check on a slave fails or a node
leaves the cluster), the error is returned to the utility and a message is
issued to the console on the master node to identify the node on which
the error occurred.
Node Shutdown
The system administrator can shut down the cluster on a given node by
invoking the cluster manager’s shutdown procedure on that node. This
terminates cluster components after cluster applications have been
stopped. VxVM supports clean node shutdown, which is the ability of
a node to leave the cluster gracefully when all access to shared volumes
has ceased. The host is still operational, but cluster applications cannot
be run on it.
The Volume Manager cluster feature maintains global state information
for each volume. This enables VxVM to accurately determine which
volumes need recovery 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 resynchronizes those volumes. If Dirty Region Logging is
active for any of those volumes, it is used.
Clean node shutdown should 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,
it could be a long time before the shutdown is successful (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, the procedure checks
all volumes in all shared disk groups on the node that is being shut down
and then either proceeds with the shutdown or fails:
• If all volumes in shared disk groups are closed, VxVM makes them
unavailable to applications. Since all nodes know that these volumes
are closed on the leaving node, no resynchronizations are performed.