What is the difference between ASL and APM and when are they used?

Problem

What is the difference between ASL and APM and when are they used?

Error Message

What's the difference between ASL and APM and when are they used?

Solution

ASLs and APMs are used in different layers of Volume Manager (VxVM).

The array support library (ASL) interacts with the DDL (user level) layer of VxVM. The array policy module (APM) interacts with the DMP (kernel component) of VxVM.

ASLs are required during the discovery phase of Volume Manager. As part of the device discovery done at the DDL layer, the ASLs are used to identify special array characteristics and to handle them appropriately.

APMs are required to handle the operational aspect of the array. As DMP will rely on the APMs when handling  the various errors returned by the array, array state changes and any special conditions for the array as the information provided by the APM will help determine what action DMP might take.