VERITAS Volume Manager 3.1 Administrator's Guide
Cluster Functionality
Dynamic Multipathing (DMP)
Chapter 7 311
Dynamic Multipathing (DMP)
NOTE You may need an additional license to use this feature.
In a clustered environment where Active/Passive type disk arrays are
shared by multiple hosts, all hosts in the cluster should access the disk
via the same physical path. If a disk from an Active/Passive type shared
disk array is accessed via multiple paths simultaneously, it could lead to
severe degradation of I/O performance. This requires path failover on a
host to be a cluster coordinated activity for an Active/Passive type disk
array.
For Active/Active type disk arrays, any disk can be simultaneously
accessed through all available physical paths to it. Therefore, in a
clustered environment all hosts do not need to access a disk, via the
same physical path.
Disabling and Enabling Controllers
System maintenance tasks can be carried out using the vxdmpadm utility.
The disable utility prevents DMP from issuing I/Os through the speciļ¬ed
controller. To disable I/Os through the host disk controller c2, use the
following command:
# vxdmpadm disable ctlr=c2
Previously disabled controllers can now be enabled to accept future I/Os.
This operation succeeds only if the controller is accessible to the host and
I/O can be performed on this controller. To enable the controller that was
previously disabled, use the following command:
# vxdmpadm enable ctlr=c2
The vxdmpadm command provides information like the list of paths
connected to the disk array and the list of DMP nodes on the system. It
also lists the controllers and enclosures connected to the system. To list
all paths controlled by the DMP node c2t1d0, use the following
command:
# vxdmpadm getsubpaths dmpnodename=c2t1d0