Offline control data set

The offline control data set (OCDS) provides DFSMShsm with information about each migration and backup tape and about each data set residing on these tapes.

Offline Control Data Set (OCDS)

Required:

No, but strongly recommended. The offline control data set is required if you are using tapes in your environment.

Allocated by starter set:

Yes, see Starter set example.

Maximum record size:

6144 bytes, if you plan to you plan to use extended tape table of contents (TTOCs) at your installation. This record size allows up to 106 data set entries per record.
2040 bytes, if you need no more than 33 data set entries per record.

Requirement: The maximum record size must be 6144 bytes if you plan to use extended TTOCs. Using extended TTOCs also requires that you issue the SETSYS EXTENDEDTTOC(Y) command on each host that will share the OCDS. For more information on the SETSYS command, see z/OS DFSMShsm Storage Administration.

Data set type:

VSAM key-sequenced data set (KSDS).

Storage guidance:

See Considerations for DFSMShsm control data sets and the journal.

TTOC records are written to the OCDS. Tape Copy Needed (TCN) records are written to the OCDS if an exception occurs during duplex processing.

Control data sets are backed up at the beginning of automatic backup and are backed up differently than user data sets, depending on how you specify the SETSYS CDSVERSIONBACKUP command. For more information, see Defining the backup environment for control data sets.

For information about the control data sets in a multiple DFSMShsm-host environment, see CDS considerations in a multiple DFSMShsm host environment.