VERITAS Volume Manager 4.1 Administrator's Guide

Administering Dynamic Multipathing (DMP)

Administering DMP Using vxdmpadm

Chapter 3 143

• 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 123 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

• singleactive

This policy routes I/O down one single active path. This is the default policy 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) by allowing failover. 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

Example of Applying Load Balancing in a SAN

This example describes how to conﬁgure load balancing in a SAN environment where there

are multiple primary paths to an Active/Passive device through several SAN switches. As can

be seen in this sample output from the vxdisk list command, the device c3t2d15 has eight

primary paths:

# vxdisk list c3t2d15

Device: c3t2d15

...

numpaths: 8