Veritas Volume Manager 4.1 Administrator's Guide (HP-UX 11i v3, February 2007)

Chapter 3, Administering Dynamic Multipathing (DMP)
Administering DMP Using vxdmpadm
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Note The benefit of this policy is lost if the value is set larger than the cache size.
The default value can be changed by adjusting the value of a tunable parameter (see
“dmp_pathswitch_blks_shift” on page 411) and rebooting the system.
The next example sets the balanced I/O policy with a partition size of 2048 blocks
(2MB) on the enclosure enc0:
# vxdmpadm setattr enclosure enc0 iopolicy=balanced \
partitionsize=2048
◆ minimumq
This policy sends I/O on paths that have the minimum number of outstanding I/O
requests in the queue for a LUN. This is suitable for low-end disks or JBODs where a
significant track cache does not exist. No further configuration is possible as DMP
automatically determines the path with the shortest queue.
The following example sets the I/O policy to minimumq for a JBOD:
# vxdmpadm setattr enclosure Disk iopolicy=minimumq
◆ priority
This policy is useful when the paths in a SAN have unequal performance, and you
want to enforce load balancing manually. You can assign priorities to each path based
on your knowledge of the configuration and performance characteristics of the
available paths, and of other aspects of your system. See “Setting the Attributes of the
Paths to an Enclosure” on page 119 for details of how to assign priority values to
individual paths.
In this example, the I/O policy is set to priority for all SENA arrays:
# vxdmpadm setattr arrayname SENA iopolicy=priority
◆ round-robin
This policy shares I/O equally between the paths in a round-robin sequence. For
example, if there are three paths, the first I/O request would use one path, the second
would use a different path, the third would be sent down the remaining path, the
fourth would go down the first path, and so on. No further configuration is possible
as this policy is automatically managed by DMP. This is the default policy for A/PC
configurations with multiple active paths per controller.
The next example sets the I/O policy to round-robin for all Active/Active arrays:
# vxdmpadm setattr arraytype A/A iopolicy=round-robin