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406 Administering cluster functionality
Overview of cluster volume management
Local detach policy
Caution: Do not use the local detach policy if you use the VCS agents that
monitor the cluster functionality of Veritas Volume Manager, and which are
provided with Veritas Storage Foundation
TM
for Cluster File System HA and
Veritas Storage Foundation for databases HA. These agents do not notify VCS
about local failures.
The local detach policy is designed to support failover applications in large
clusters where the redundancy of the volume is more important than the
number of nodes that can access the volume. If there is a write failure on a slave
node, the master node performs the usual I/O recovery operations to repair the
failure, and additionally contacts all the nodes to see if the disk is still acceptable
to them. If the write failure is not seen by all the nodes, I/O is stopped for the
node that first saw the failure, and the application using the volume is also
notified about the failure. The volume is not disabled.
If required, configure the cluster management software to move the application
to a different node, and/or remove the node that saw the failure from the
cluster. The volume continues to return write errors, as long as one mirror of
the volume has an error. The volume continues to satisfy read requests as long
as one good plex is available.
If the reason for the I/O error is corrected and the node is still a member of the
cluster, it can resume performing I/O from/to the volume without affecting the
redundancy of the data.
See “Setting the disk detach policy on a shared disk group” on page 425 for
information on how to use the
vxdg command to set the disk detach policy on a
shared disk group.
The table, “Cluster behavior under I/O failure to a mirrored volume for different
disk detach policies,” summarizes the effect on a cluster of I/O failure to the
disks in a mirrored volume:
Table 13-3 Cluster behavior under I/O failure to a mirrored volume for different
disk detach policies
Type of I/O failure Local
(diskdetpolicy=local)
Global
(diskdetpolicy=global)
Failure of path to one
disk in a volume for a
single node
Reads fail only if no plexes
remain available to the
affected node. Writes to the
volume fail.
The plex is detached, and I/O
from/to the volume continues.
An I/O error is generated if no
plexes remain.