Automatic class selection (ACS) routines determine, validate, or override the existing values that are assigned for the storage group, storage class, management class, and data class constructs for a collection. The classes assigned are those assigned to the collection or those that are explicitly stated on the OSREQ request to store or change an object. ACS routines are called to verify the storage class and management class that are stated on the OSREQ request. The ACS routines can accept the stated class, select a different one, or reject the stated class and return an error code.
Every object belongs to a collection. Each collection belongs to only one Object storage group. When an object is stored, it is automatically assigned to the Object storage group to which its specified collection belongs. Every object, when it is stored, is assigned a storage class and a management class. See Figure 1 for a diagram of this process.
Recommendation: For objects that reside on tape volumes, having the ACS routines alter the data class that was originally assigned to the tape volume through the SETOAM statement at MVS scratch tape allocation is not recommended. For more information, see the recommendation regarding data class and ACS routines.