Understanding the Automatic Class Selection Process

The system processes that result in the invocation of ACS routines are:

Allocation of new data sets that are eligible to be SMS-managed.
Restriction: The data class routine can also be executed for data sets that are not eligible to be system-managed. However, if the ACS routine detects a data set that is not eligible to be system-managed, the following should occur:
- If a data class is specified, it should be assigned to that data set.
- If a storage class or management class is specified, the allocation should fail followed by an error message.
Conversion of SMS volumes and data sets
DFSMShsm recall and recover
DFSMSdss COPY, RESTORE, and CONVERTV commands
Access method services ALLOCATE, DEFINE, and IMPORT commands
Object access method (OAM) STORE, CHANGE, and CTRANS.

Table 1 summarizes what happens to each of the SMS constructs when automatic class selection takes place.

Table 1. Automatic Class Selection Process
Step	Action
1	Assign data class: Step Action A Call data class ACS routine, if it exists, to assign a data class. B Call data class ACS installation exit. See note. C Validate data class name. ACS services ensures that the name assigned is for a defined data class.
2	Assign storage class: Step Action A Call storage class ACS routine to assign a storage class B Call storage class ACS installation exit. See note. C Validate storage class name. ACS services ensures that the name assigned is for a defined storage class. D Check user's authority to determine if she or he is allowed to use the storage class.
If no storage class is assigned in the previous step, the following steps are not taken:
3	Assign management class Step Action A Call management class routine to assign a management class. B Call management class ACS installation exit. See note. C Validate management class name. ACS services ensures that the name assigned is for a defined management class. D Check user's authority to determine if she or he is allowed to use the management class.
4	Assign storage group Step Action A Call storage group ACS routine to assign a storage group. B Validate the storage group name. ACS services ensures that the name assigned is for a defined storage group.
Note: The ACS installation exit routines can override the class assignments made in the ACS routine. Also, ACS installation exit routines can alter the input to ACS routines and recall them one time. The installation exit is not recalled when it recalls the ACS routine.