JES3 considerations

When you implement DFSMShsm in a JES3 environment, you must observe certain practices and restrictions to ensure correct operation:

For a period of time after the initialization of JES3 and before the initialization of DFSMShsm, all JES3 locates will fail. To reduce this exposure:
- Start DFSMShsm as early as possible after the initialization of JES3.
- Specify the SETSYS JES3 command as early as possible in the startup procedure and before any ADDVOL commands.
Specify JES3 during DFSMShsm startup when DFSMShsm is started in a JES3 system. This avoids an error message being written when DFSMShsm receives the first locate request from the JES3 converter/interpreter.
Depend on the computing system catalog to determine the locations of data sets.
Do not allocate the control data sets and the JES3 spool data set on the same volume because you could prevent DFSMShsm from starting on a JES3 local processor.
All devices that contain volumes automatically managed or processed by DFSMShsm must be controlled by JES3. All volumes managed by DFSMShsm (even those managed by command) should be used on devices controlled by JES3.
DFSMShsm must be active on the processing units that use volumes managed by DFSMShsm and on any processing unit where JES3 can issue the locate request for the setup of jobs that use volumes managed by DFSMShsm.

The specification of JES3 places a constraint on issuing certain DFSMShsm commands. When you use JES2, you can issue ADDVOL, DEFINE, and SETSYS commands at any time. When you specify JES3, you must issue ADDVOL commands for primary volumes, DEFINE commands for pools (except aggregate recovery pools), and the SETSYS JES2 or SETSYS JES3 commands in the ARCCMDxx member. In addition, if you are naming tape devices with esoteric names, you must include the SETSYS USERUNITTABLE command in the ARCCMDxx member before the ADDVOL command for any of the tapes that are in groups defined with esoteric names.

If you specify JES3 but the operating system uses JES2, DFSMShsm is not notified of the error. However, DFSMShsm uses the rules that govern pool configuration for JES3, and one or both of the following situations can occur:

Some ADDVOL, SETSYS, and DEFINE commands fail if they are issued when they are not acceptable in a JES3 system.
Volumes eligible for recall in a JES2 system might not qualify for the DFSMShsm general pool and, in some cases, are not available for recall in the JES3 system.

When you use DFSMShsm and JES3, the usual configuration is a symmetric configuration. A symmetric configuration is one where the primary volumes are added to DFSMShsm in all processing units and the hardware is connected in all processing units. Because of the dynamic reconfiguration of JES3, you should use a symmetric JES3 configuration.

If your device types are 3490, define the special esoteric names SYS3480R and SYS348XR to JES3. This may only be done after the system software support (JES3, DFP, and MVS™) for 3490 is available on all processing units.

The main reason for this is conversion from 3480s, to allow DFSMShsm to convert the following generic unit names to the special esoteric names:

3480 (used for output) is changed to SYS3480R for input drive selection. SYS3480R is a special esoteric name that is associated with all 3480, 3480X, and 3490 devices. Any device in this esoteric is capable of reading a cartridge written by a 3480 device.
3480X (used for output) is changed to SYS348XR for input drive selection. SYS348XR is a special esoteric name that is associated with all 3480X and 3490 devices. Any device in this esoteric is capable of reading a cartridge written by a 3480X device.

Note:

Because of the DFSMShsm use of the S99DYNDI field in the SVC99 parameter list, the JES3 exit IATUX32 is not invoked when DFSMShsm is active.
By default, JES3 support is not enabled for DFSMShsm hosts defined using HOSTMODE=AUX. Contact IBM support if you require JES3 support for AUX DFSMShsm hosts. When JES3 for AUX DFSMShsm hosts is enabled, you should start the main DFSMShsm host before starting any AUX hosts and stop all AUX hosts before stopping the main host.