Volume reference and unit affinity

When both VOL=REF and UNIT=AFF are specified, VOL=REF processing takes precedence over UNIT=AFF. The &UNIT read-only variable may contain blanks or 'AFF= ', depending on the disposition of the referenced DD.

Recommendation: When specifying both VOL=REF and UNIT=AFF, ensure that the ACS routines check for &ANYVOL='REF=ST', 'REF=SD' or 'REF=NS' before checking the &UNIT read-only variable. This ensures that the ACS routines select the correct classes.

Unlike volume reference processing, in which the storage class is produced from the REF'ed DD, unit affinity processing allows you to break the affinity by setting a different storage class. Even though the AFF'ed DD's storage class is passed as input to the storage class routine, the storage class routine must set a valid storage class for the job to run successfully.