Veritas Volume Manager 5.0 Administrator's Guide (September 2006)

143Administering dynamic multipathing (DMP)
Administering DMP using vxdmpadm
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
This is the default I/O policy for A/A arrays.
■ 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 139 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.
The next example sets the I/O policy to round-robin for all Active/Active arrays:
# vxdmpadm setattr arraytype A/A iopolicy=round-robin
This is the default I/O policy for A/P and Asymmetric Active/Active (A/A-A) arrays.
■ singleactive
This policy routes I/O down the single active path. This policy can be configured for
A/P arrays with one active path per controller, where the other paths are used in case
of failover. If configured for A/A arrays, there is no load balancing across the paths,
and the alternate paths are only used to provide high availability (HA). If the
currently active path fails, I/O is switched to an alternate active path. No further
configuration is possible as the single active path is selected by DMP.
The following example sets the I/O policy to singleactive for JBOD disks:
# vxdmpadm setattr arrayname DISK iopolicy=singleactive