Tape disposition
Tape disposition at the end of the data set or volume can be affected by the DISP parameter of the DD statement. This implied disposition can be overridden by a positioning parameter of the OPEN, FEOV, or CLOSE macro. The OPEN macro controls positioning after an end-of-volume condition (multivolume data sets), unless overridden by the FEOV macro. The CLOSE macro controls positioning at the end of the data set.
The positioning parameters of the OPEN, FEOV, and CLOSE macro instructions
are:
- LEAVE
- Position the volume at the logical end of the data set just read or written. If the data set has been read backward, the logical end is the physical beginning of the data set.
- REREAD
- Position the volume at the logical beginning of the data set just read or written. When the data set exists on more volumes than there are units available, the REREAD parameter should not be used with the OPEN macro instruction—it may adversely affect the time required to mount the tapes. REREAD cannot be specified for FEOV.
- REWIND
- Rewind the volume to the load point. REWIND cannot be specified for OPEN or CLOSE TYPE=T.
- DISP
- Perform the disposition processing that was requested. This can be LEAVE, REWIND, or REWIND and UNLOAD, depending on the volume attributes. DISP cannot be specified for FEOV.
The CLOSE macro has the following additional operand that allows
you to release tape data sets and the volumes on which they reside:
- FREE
- Release the data set associated with this DCB. FREE specifies that the data set is to be released for use by another job and that the device on which the data set is mounted can be freed for allocation to another job.
DISP is the default.
If necessary, the specified volume disposition can be overridden by the system. However, you need not be concerned; the system automatically requests the mounting and demounting of volumes depending on the availability of devices at a particular time.