150Administering dynamic multipathing (DMP)

Administering DMP using vxdmpadm

■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

This is the default I/O policy for Active/Active (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 146 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-robinfor all Active/Active arrays:

#vxdmpadm setattr arraytype A/A iopolicy=round-robin

This is the default I/O policy for Active/Passive (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: