Non-data set stacking allocations

The following considerations apply when UNIT=AFF is used to reduce the number of units for a job, instead of data set stacking.

When unit affinity is specified on a DD statement, three new values are set depending on the unit of the AFF'ed DD. The following example explains how these values are set. In this example, DD1 is directed to SMS DASD, and DD2 is directed to SMS tape.

     //DD1 DD UNIT=SYSDA,DISP=NEW,..
     //DD2 DD UNIT=AFF=DD1,DISP=NEW,..
     //DD3 DD UNIT=AFF=DD2,DISP=NEW,..
     //DD4 DD UNIT=AFF=DD1,DISP=NEW,...

DD Being Processed	&UNIT Read-Only Variable Value
DD1	'SYSDA'
DD2	'AFF=SMSD' (if DD1 is directed to SMS DASD)
DD3	'AFF=SMST' (if DD2 is directed to SMS tape)
DD4	'AFF=SMSD' (if DD1 is directed to SMS DASD)

With the exception of the JES3 environment, ACS routines are called multiple times. When the ACS routines are invoked by the JES3 PRESCAN processing, the &UNIT read-only variable are set to AFF= for DD2, DD3, and DD4. The ACS routines are invoked again later during the allocation process with the values shown in the example.

Table 1 illustrates how &LIBNAME, &STORGRP, &ALLVOL, &ANYVOL, and &STORCLAS are set. These read-only variables are set depending on the value of the AFF'ed DD (for example, DD1 if DD2 is being processed) or the VOLSER value on the AFF'ing DD (DD2).

Table 1. AFFing DD Volser Values
AFFing DD Volser Values			&LIBNAME	&STORGRP	&ALLVOL	&ANYVOL	&STORCLAS
DD2 volser= V2	V2 = lib resident		libnamesofV2	sgnameofV2	V2	V2	blank
DD2 volser= V2	V2/= lib resident		blank	blank	V2	V2	blank
DD2 volser= blank	DD1= SMSDASD		blank	sgnameofDD1	blank	blank	scnameofDD1
	DD1= nonSMS		blank	blank	blank	blank	blank
	DD1=SMSTAPE	DD1volser =V1	libnameofV1	sgnameofV1	blank	blank	blank
	DD1=SMSTAPE	DD1volser =blank DISP=NEW	blank	blank	blank	blank	blank

Note: When both the AFFing DD and the AFFed DD are DISP=NEW, the storgrp and the library values will not be available when ACS routines are being processed for the AFFing DD.