The user can control the number of subtasks generated by means of the PARALLEL-RUNS operand. Interpretation of the value specified for PARALLEL-RUNS is subject to the following rules:
The number of subtasks that can be used to continue, read or copy an existing backup file must not exceed the number of subtasks that were actually used when the save file was created. This also applies when an existing save file is extended without multiplexing operation.
If multiplexing operation is active, an existing save file with a higher multiplexing factor than the predecessor save versions can be continued. Thus the number of ARCHIVE subtasks can be higher but not the number of devices.
If the number of subtasks used for COPY activities on a save file is less than the number of subtasks that were actually used when the save file was created it can happen (with SEVERAL-SVID) that the volume is rewound to the beginning-of-tape marker once more during processing.
Notes
If the number of packets generated is less than the number of ARCHIVE subtasks requested, some ARCHIVE subtasks will be generated which do not get used.
The number of ARCHIVE subtasks used to create save files should be calculated such that the same number of subtasks can be used for COPY activities from these save files, although the number of tape devices available at the time of copying must be taken into account.