Limiting data that is written to a cartridge-type device

When you want to direct data to a cartridge-type tape volume within a single-file-format tape environment, you can specify the percent full from 1 to 9999 on the SETSYS TAPEUTILIZATION(UNITTYPE(unit) PERCENTFULL(pct)) command. When the percent full is reached, DFSMShsm forces end-of-volume function on that volume. This command limits the amount of data that is written on a cartridge-type tape volume, which ensures that the tape can be copied with the TAPECOPY command. This also ensures that the original and the alternate tapes are identical when they are duplexed.

If your installation is backing up or migrating many small data sets, you might not be making full use of newer high capacity tape volumes. Here, it is recommended that your installation use extended tape table of contents (TTOCs). Doing so allows DFSMShsm to write as many as 1,060,000 data sets on a single migration tape or backup tape, if the data sets will fit. In previous releases of z/OS®, this number was limited to 330,000 data sets.

To use extended TTOCs, you must:

For information about defining the OCDS, see z/OS DFSMShsm Implementation and Customization Guide.

Note:
  1. When you specify SETSYS DUPLEX for either backup or migration, or both, and you specify the NOLIMIT parameter for your tapes, PERCENTFULL is automatically set to 97%. If you designate a specific percentage, such as 100, DFSMShsm uses the percentage that you specify.
  2. Other effects of specifying the NOLIMIT parameter with the TAPEUTILIZATION command are that only one buffer is used for recycle processing rather than three, and no action is taken to reduce data set tape volume spanning.
  3. You can use the following table to determine the PERCENTFULL value on the SETSYS TAPEUTILIZATION(UNITTYPE(unit)PERCENTFULL(pct)) command.
    Table 1. Cartridge Percentages, by Output Device and Length
    Output Device IBM® Standard Length Cartridge Percentages IBM Enhanced Length Cartridge Percentages Other Cartridge Length Percentages
    3490E native attached drive 1–100 1–100 1–9999, when compared to the IBM 3490E cartridge
    3590B native attached drive 1–100 1–100 1–9999, when compared to the IBM 3590 cartridge
    3590B emulating 3490E 1–100 1–100 1–9999, when compared to the IBM 3590 cartridge
    3590E emulating 3490E or 3590B 1–100 1–100 1–9999, when compared to the IBM 3590 cartridge
    3590 Model H emulating a 3590 Model B or 3490E 1–100 1–100 1–9999, when compared to the IBM 3590 cartridge
    3592 Model J emulating 3490E or 3590B 1–100 N/A N/A
    3592 Model E-05 emulating 3590B 1–100 N/A N/A
    3592 Model E-06 emulating 3590B 1–100 N/A N/A
    Note: If your environment consists of different technology 3590 tape devices configured as stand-alone (non-SMS tape), you must associate an esoteric name with each type of device. You also must request that DFSMShsm use the esoteric names rather than the generic names. This also applies to a mixed 3490 environment.
  4. If backup or migration is using a system-managed tape library, specify the LIBRARYBACKUP or LIBRARYMIGRATION parameters with the SETSYS TAPEUTILIZATION command.
  5. 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 example, to use virtual tapes for backup and migration volumes, you could enter the following commands: 
    SETSYS TAPEUTILIZATION(LIBRARYBACKUP PERCENTFUL(97))
SETSYS TAPEUTILIZATION(LIBRARYMIGRATION PERCENTFUL(97))

Related reading

For more information about the LIBRARYMIGRATION parameters, see TAPEUTILIZATION: Specifying the desired tape utilization.

Parent topic: Managing DFSMShsm media