The data class and storage class ACS routines process all new allocations, not just ones for direct access storage. You must ensure that non-DASD requests for allocations are not assigned a non-null storage class. Define your esoteric names for DASD, such as SYSDA, in a FILTLIST that includes all valid unit types. Check the UNIT against this FILTLIST. If the UNIT is not valid, assign a null storage class.