Examples

Example 1: The following statements define the relationship among the names supplied for a user's tape drives. Assume the user's JES3 complex includes 3400-4, 2400-4, and 2400 tape drives. The esoteric (user-defined) name TAPE encompasses all tape drives in the complex, while the esoteric name DUALDEN encompasses only dual-density tape drives. (Statement numbers to the left of each statement are for the purpose of discussion only.)

HWSNAME,TYPE=(TAPE,DUALDEN,3400-4,3400-3,2400-4,2400-3,2400)
HWSNAME,TYPE=(DUALDEN,3400-4,3400-3,2400-4,2400-3,TAPE)
HWSNAME,TYPE=(2400,3400-4,3400-3,2400-4,2400-3,DUALDEN,TAPE)
HWSNAME,TYPE=(2400-4,2400-3,3400-4,3400-3,DUALDEN,TAPE)
HWSNAME,TYPE=(3400-4,3400-3,DUALDEN,TAPE)
HWSNAME,TYPE=(2400-3,2400-4,3400-4,3400-3,DUALDEN,TAPE)
HWSNAME,TYPE=(3400-3,3400-4,DUALDEN,TAPE)

Statement 1 defines all the device names that can be used to satisfy a request for UNIT=TAPE. Note that both generic and esoteric alternate names are used. Statement 2 defines all the names that can be used to allocate a UNIT=DUALDEN request. Note that 2400 is not listed because it is not a dual-density device and there are 2400s in the complex. On the other hand, 2400-3 and 3400-3 do appear as alternates because there are no devices of those types in the complex, so a request for one always results in the allocation of a dual-density device. TAPE also appears as an alternate because TAPE could be used to satisfy a DUALDEN request.

In statement 3, all device names are shown as valid alternates for 2400. This is in keeping with allocation rules that allow a single-density request to be satisfied by certain dual-density devices. Statements 4 and 5 define the alternate names for the respective dual-density generic names. Note that 3400-4 is an alternate for 2400-4, but that the reverse is not true. This is because a 2400-4 cannot be used to satisfy a request for a 3400-4.

Statements 6 and 7 define single-density device names that are entered in the catalog for data sets created on 2400-4 or 3400-4 dual-density devices at 1600 BPI.

Assuming the HWSNAME input shown, the following JCL results in one device, a 2400-4, being allocated for the entire job.

//TST JOB
//STPA EXEC PGM=IEFBR14
//DDA1 DD DSN=A,UNIT=2400,VOL=SER=V1,DISP=OLD
//STPB EXEC PGM=IEFBR14
//DDB1 DD DSN=B,UNIT=DUALDEN,VOL=SER=V2,DISP=OLD
//STPC EXEC PGM=IEFBR14
//DDC1 DD DSN=C,UNIT=2400-4,VOL=SER=V3,DISP=OLD

According to the HWSNAME entries, a 2400-4 can be used to satisfy all unit requests in this job. That is, 2400-4 is an acceptable alternative to the DDA1's request for a 2400 unit (HWSNAME card 3) and DDB1's request for a DUALDEN unit (HWSNAME statement 2). One 2400-4 unit, therefore, will be assigned for DDA1 and this will be propagated to the remainder of the requests.

By contrast, if you want to completely separate the single-density and dual-density drives, the following could be provided.

HWSNAME,TYPE=(TAPE,DUALDEN,3400-4,3400-3,2400-4,2400-3)
HWSNAME,TYPE=(DUALDEN,3400-4,3400-3,2400-4,2400-3,TAPE)
HWSNAME,TYPE=(3400-4,3400-3,DUALDEN,TAPE)
HWSNAME,TYPE=(2400-4,2400-3,3400-4,3400-3,DUALDEN,TAPE)
HWSNAME,TYPE=(TAPSING,2400)
HWSNAME,TYPE=(2400,TAPSING)

With this HWSNAME input, the same JCL would result in two tape drives being assigned: one 2400 drive, to satisfy the DDA1 request, and the 2400-4 drive to be used for both the DDB1 and DDC1 requests. Note that the single-density tape drives defined as alternates to the dual-density tape drives do not violate the decision to separate dual-density and single-density devices. As in the previous set of HWSNAME statements, these single-density tape drives are equivalent to the dual-density tape drives because a request for one of them will always result in the allocation of a dual-density device.

Example 2: Assume that an installation has 3400-5 and 3400-6 tape drives. The 3400-5 single density tape drive should not be defined as an alternate for the 3400-6 dual density tape drive.

For example, consider the following JCL:

//STEPA EXEC PGM=X
//DD1 DD UNIT=3400-5,VOL=SER=VOL001,DISP=OLD
//DD2 DD DSN=ABC,UNIT=AFF=DD1,DISP=OLD

Assume that data set ABC is cataloged as residing on volume VOL003 and requiring a device type of 3400-6.

In a complex where both the 3400-5 and 3400-6 devices exist and are JES3-managed, the following HWSNAME statements should be used:

HWSNAME,TYPE=(3400-5,3400-6)
HWSNAME,TYPE=(3400-6)

This indicates that a 3400-6 is an acceptable alternate for a 3400-5, but the 3400-5 is not an acceptable alternative for a 3400-6. The UNIT affinity in the example, therefore, is negated because the referenced 3400-5 is not a valid subset of the cataloged unit (3400-6). Two devices would be required under these circumstances.

If the JES3 complex contained only 3400-6 tape drives, then the volume requested by DD1 would have to be mounted on a 3400-6 and the unit affinity on DD2 would be valid. However, the HWSNAME information would not allow JES3 to honor the affinity and two devices (3400-6) would still be required. But by modifying the HWSNAME statements as follows, the user could enable JES3 to allocate devices more efficiently:

HWSNAME,TYPE=(3400-5,3400-6)
HWSNAME,TYPE=(3400-6,3400-5)

Because the installation contains only dual density devices (3400-6), any device request can be satisfied by any available unit.