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

severely degrade I/O performance (sometimes referred to as the ping-pong effect).
Path failover on a single cluster node is also coordinated across the cluster so that
all the nodes continue to share the same physical path.
Prior to release 4.1 of VxVM, the clustering and DMP features could not handle
automatic failback in A/P arrays when a path was restored, and did not support
failback for explicit failover mode arrays. Failback could only be implemented
manually by running the vxdctl enable command on each cluster node after the
path failure had been corrected. From release 4.1, failback is now an automatic
cluster-wide operation that is coordinated by the master node. Automatic failback
in explicit failover mode arrays is also handled by issuing the appropriate low-level
command.
Note: Support for automatic failback of an A/P array requires that an appropriate
ASL (and APM, if required) is available for the array, and has been installed on
the system.
See “Discovering disks and dynamically adding disk arrays” on page 85.
For Active/Active type disk arrays, any disk can be simultaneously accessed
through all available physical paths to it. In a clustered environment, the nodes
do not all need to access a disk via the same physical path.
See “How to administer the Device Discovery Layer” on page 87.
See “Configuring array policy modules” on page 196.
About enabling or disabling controllers with shared disk groups
Prior to release 5.0, VxVM did not allow enabling or disabling of paths or
controllers connected to a disk that is part of a shared Veritas Volume Manager
disk group. From VxVM 5.0 onward, such operations are supported on shared
DMP nodes in a cluster.
Disabling multi-pathing and making devices invisible
to VxVM
Use this procedure to prevent a device from being multi-pathed by the VxVM
DMP driver (vxdmp), or to exclude a device from the view of VxVM.
Administering Dynamic Multi-Pathing
Disabling multi-pathing and making devices invisible to VxVM
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