Automatic Class Selection (ACS) Installation Exits

Each automatic class selection (ACS) routine, except the one for storage group, has an ACS installation exit that lets you write exit routines for additional capabilities. The exit routines you write are processed when the corresponding ACS routine is called.

The ACS installation exits reside in SYS1.LPALIB and are listed in Table 1. ACS routines are part of system-managed storage and are described inz/OS DFSMSdfp Storage Administration .

Table 1. ACS Replaceable Modules
Module Name	Description	When Available
IGDACSDC	Data class exit	After the data class ACS routine has executed
IGDACSSC	Storage class exit	After the storage class ACS routine has executed
IGDACSMC	Management class exit	After the management class ACS routine has executed

ACS routines and ACS installation exit routines can perform many of the same functions. Wherever possible, use ACS routines because, compared with ACS installation exit routines, they are relatively easy to write, maintain, and modify. You do not need to re-IPL the system after you create or modify ACS routines; because ACS exit routines reside in SYS1.LPALIB, you must re-IPL after you change them. However, only the ACS installation exit routines can be used to:

Call other programs.
Call other subsystems.
Write SMF records.
Write GTF trace records.
Take SVC dumps.
Maintain large, easily searched tables of information in storage.

ACS services allow an installation-written exit routine to take control after the ACS routine has processed. An ACS installation exit routine can override any values assigned by the ACS routine and can return messages to the batch job, started task, or TSO/E user.

An ACS installation exit routine can recall an ACS routine one time to determine a new value for an SMS class. This new value can be assigned to a data set or be used for comparison with the original value assigned in step 1, Table 1. Use the ACS interface routine to invoke an ACS routine. The parameter list that is passed to your exit routine, as shown in Figure 1, contains a field (ACSPACS) that points to the ACS interface routine.