z/OS JES3 Initialization and Tuning Reference
z/OS JES3 Initialization and Tuning Reference
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Parameters z/OS JES3 Initialization and Tuning Reference SA32-1005-00 |
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Special care must be taken when specifying alternate names. The alternate device must be compatible, for MVS™ allocation purposes, with the device specified by the devname subparameter. Thus, you may not specify a 2314 DASD as an alternate name for a 3330 DASD, and you may not specify 3330 as an alternate name for 2314. Similarly, you may not specify a 2400-series tape drive as an alternate for a 3400-series tape drive. You may, however, specify a 3400-series tape drive as an alternate for a 2400-series tape drive. The following figure shows which tape drives MVS considers acceptable alternates to a request for a specific tape drive.
If your JES3 complex includes dual-density tape drives, your initialization stream must include certain HWSNAME statements to achieve the best use of high-watermark setup. These statements are necessary because of the way MVS catalogs data sets that you requested to be created on dual-density tape drives. MVS determines which single-density tape drive (of the same series as the dual-density tape drive) uses the same density as the data set. MVS then catalogs the data set as requiring that single-density tape drive. For example, if you create a data set on a 3400-6 dual-density tape drive at 6250 BPI, MVS catalogs the data set as requiring a 3400-5 tape drive (single density, 6250 BPI). MVS catalogs data sets this way regardless of whether your installation includes the single-density tape drive. This cataloging method aids the device allocation process, because a request for a single-density device has more acceptable alternates for allocation than a request for a dual-density device. (See Table 1.) Thus, in the above example, MVS may allocate either a 3400-5 or a 3400-6 for the data set. If the data set had been cataloged as requiring a 3400-6, MVS could allocate only a 3400-6. Note: One special case exists in which MVS catalogs
a data set as requiring a dual-density device. Because there is no
single-density tape drive in the 3400-series with a density of 800
BPI, a data set created on a 3400-4 at 800 BPI is cataloged as requiring
a 3400-4.
To use high-watermark setup, you must let JES3 know which device types are valid for HWS. If you have dual-density tape drives in your complex, you must include HWSNAME statements for all single-density tape drives that appear in the catalog as required devices for data sets. Otherwise, JES3 considers requests for those devices, whether through data set catalog entries or otherwise, ineligible for HWS. Refer again to the example in which MVS catalogs
a data set as requiring a 3400-5 tape drive when the data set was
created on a 3400-6 tape drive at 6250 BPI. If you do not have any
3400-5 devices in your complex, MVS allocates
a 3400-6 device for that data set. (See Table 1.) If you want jobs using that cataloged data set to be eligible
for HWS, you must tell JES3 that a request for a 3400-5 is a valid
HWS request and that it is equivalent to a request for a 3400-6. Code
your HWSNAME statements so that the 3400-6 and 3400-5 appear as alternates
to each other:
See Table 2 for sample HWSNAME statement specifications for various configurations of 3400-series tape drives. The figure shows only the recommended generic device type specifications; you may add any esoteric names appropriate for your installation. Note that when your complex includes a single-density tape drive, the allocation of the single-density device cannot satisfy a request for the dual-density device. Therefore, the two device types are not equivalent. You must not specify the single-density device as an alternate to the dual-density device when the complex includes the single-density device. Use the sample HWSNAME statements for 3400-series tape drives as a guideline for writing your HWSNAME statements for 2400-series tape drives.
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