Foundation Block Parameters

DDNAME=symbol

The name of the data definition (DD) statement that describes the data set to be processed. This parameter is required and must be supplied before your program issues the OPEN macro. You can code a dummy value and change it before issuing OPEN.

MACRF=E

The EXCP or EXCPVR macro instruction is to be used in processing the data set. This operand must be coded and must be supplied before your program issues the OPEN macro.

REPOS=Y or N

Magnetic tape volumes: This parameter indicates to the system whether the user is keeping an accurate block count. (Maintain the block count in the DCBBLKCT field.) The system ignores this parameter when the program is executing and the device is not magnetic tape.

The EOV and CLOSE functions can record the block count in the IBM® standard or ISO/ANSI standard trailer labels.

On input, the EOV and CLOSE functions can compare the DCB block count with the block count in the standard trailer labels to detect missing or duplicate blocks. This is supported on reel and cartridge tapes.

On input or output, the EOV and CLOSE functions can compare the DCB block count with the block count calculated from tape cartridge subsystems to detect missing or duplicate blocks. The system does this for any label type and for unlabeled tapes. Refer to z/OS DFSMS Using Magnetic Tapes.

For magnetic tape devices with reels (not cartridges), coding REPOS=Y allows the dynamic device reconfiguration (DDR) function to move the volume to another tape drive if the drive has a failure. With a cartridge, DDR can do this without your program maintaining block count.

For magnetic tape devices with reels (not cartridges), restart requires the block count in order to restore the tape to its position at the time of the checkpoint. With a cartridge, restart can do this without requiring that you maintain a block count.

The system performs the following tasks:

Y-The count is accurate.
N-The block count is inaccurate.

If the operand is omitted, N is assumed.