Specifying how much of a tape DFSMShsm uses

For TAPECOPY command or DUPLEX option: If you are copying the contents of one tape to another with the TAPECOPY command or are using the concurrent creation option DUPLEX, you need to be aware of minor inconsistencies that can exist in the length of cartridge-type tapes. Because the TAPECOPY command copies the entire contents of one tape to another, it is important that enough media is available to copy the entire source tape to its target. Therefore, when you are copying tapes with the TAPECOPY command, use the default options (the equivalent of specifying the TAPEUTILIZATION command with the PERCENTFULL option of 97 percent). DFSMShsm marks the end of volume when tapes are 97 percent full. When you use the duplex option, it is recommended that you use the value 97% to ensure that you can write the same amount of data to both tapes. During duplexing, the NOLIMIT parameter of TAPEUTILIZATION will be converted to the default of 97%.

If you are not copying tapes with the TAPECOPY command and you are not creating two tapes using the DUPLEX option, you can specify the TAPEUTILIZATION command with a PERCENTFULL option of 100%.

Tape utilization is specified differently for library environments than for nonlibrary environments. Table 1 shows how tape utilization is specified for both library and nonlibrary environments.

Table 1. Specifying Tape Utilization. Tape utilization is specified differently for library and nonlibrary environments. In this example, DFSMShsm marks end of volume when the tape is 97% full.
Tape Environment	Specifying Tape Utilization
Nonlibrary	SETSYS TAPEUTILIZATION(UNITTYPE(3590-1) PERCENTFULL(97))
SMS-Managed Tape Library	SETSYS TAPEUTILIZATION(LIBRARYBACKUP PERCENTFULL(97)) or SETSYS TAPEUTILIZATION(LIBRARYMIGRATION - PERCENTFULL(97))

Tip: You can substitute an esoteric unit name for the generic device name shown in the preceding example.

Note: Virtual tape systems should generally use a PERCENTFULL value of 97% unless a bigger value is needed to account for virtual tapes larger than the nominal 400 MB standard capacity MEDIA1 or 800 MB enhanced capacity MEDIA2 tapes. In the case of the newer virtual tape systems (TS7700 Release 1.4 and above), where DFSMShsm derives media capacity by checking the mounted virtual tape, DFSMShsm allows a PERCENTFULL value up to 110%. Anything larger is reduced to 100%. For older virtual tape systems, where DFSMShsm cannot dynamically determine virtual tape capacity, PERCENTFULL values larger than 110% are honored. For a detailed description of the SETSYS TAPEUTILIZATION command, see z/OS DFSMShsm Storage Administration.

For 3590 Model E devices: If you are using IBM® 3590-Ex models in either native or 3490 emulation mode, DFSMShsm defaults to writing 97% of the true cartridge’s capacity and you probably do not need to specify TAPEUTILIZATION for those output devices. If you are using IBM 3590-Bx drives (128-track recording) to emulate 3490 devices, you need to specify TAPEUTILIZATION PERCENTFULL of a much larger value than the default. The recommended value is 2200, which instructs DFSMShsm to use 2200% of the logical cartridge’s capacity as the capacity of tapes that are written to the supplied unit name. For a detailed discussion of the SETSYS TAPEUTILIZATION command, see z/OS DFSMShsm Storage Administration.

Note: For 3490 emulation by other hardware vendors, check with the vendors to determine which percentage should be specified.

For 3592 devices: Customers requiring very fast access to data on a MEDIA5 , MEDIA9, or MEDIA11 tape can exploit the 3592 performance scaling feature. Within DFSMShsm, performance scaling applies to single file tape data set names in both tape libraries and stand-alone environments.

Through the ISMF Data Class application, the performance scaling option uses 20% of the physical space on each tape and keeps all data sets closer together and closer to the initial load point. Performance scaling also allows the same amount of data to exist on a larger number of tapes, so more input tasks can run at the same time. This can increase the effective bandwidth during operations that read data from the tape. Alternatively, performance segmentation allows the use of most of the physical media while enhancing performance in the first and last portions of the tape.

As an alternative to using MEDIA5 , MEDIA9, or MEDIA11 tapes with performance scaling, consider using MEDIA7 or MEDIA13 tapes for high performance functions. Your MEDIA5 , MEDIA9, or MEDIA11 tapes could then be used to their full capacity.

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