VERITAS Volume Manager 4.1 Administrator's Guide

Administering Dynamic Multipathing (DMP)

Administering DMP Using vxdmpadm

Chapter 3 149

Conﬁguring Array Policy Modules

An array policy module (APM) is a dynamically loadable kernel module that may be provided

by some vendors for use in conjunction with an array. An APM deﬁnes procedures to:

• Select an I/O path when multiple paths to a disk within the array are available.

• Select the path failover mechanism.

• Select the alternate path in the case of a path failure.

• Put a path change into effect.

• Respond to SCSI reservation or release requests.

DMP supplies default procedures for these functions when an array is registered. An APM

may modify some or all of the existing procedures that are provided by DMP or by another

version of the APM.

You can use the following command to display all the APMs that are conﬁgured for a system:

# vxdmpadm listapm all

The output from this command includes the ﬁle name of each module, the supported array

type, the APM name, the APM version, and whether the module is currently in use (loaded).

To see detailed information for an individual module, specify the module name as the

argument to the command:

# vxdmpadm listapm module_name

To add and conﬁgure an APM, use the following command:

# vxdmpadm -a cfgapm module_name [attr1=value1 [attr2=value2 ...]]

The optional conﬁguration attributes and their values are speciﬁc to the APM for an array.

Consult the documentation that is provided by the array vendor for details.

NOTE By default, DMP uses the most recent APM that is available. Specify the -u

option instead of the -a option if you want to force DMP to use an earlier

version of the APM. The current version of an APM is replaced only if it is not

in use.

Specifying the -r option allows you to remove an APM that is not currently loaded:

# vxdmpadm -r cfgapm module_name

For more information about conﬁguring APMs, see the vxdmpadm(1M) manual page.