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The CTTGVL utility assigns a volume to a specific data set before the data set is allocated. The utility returns a volume serial number (according to user specifications) for the file that the user wants to create.
When the CTTGVL utility returns a volume serial number, the volume is assigned a status of In-Use. This status prevents selection of the volume by other users. When a data set is written to the selected volume, the In-Use status is removed from the volume.
If, for some reason, (for example, because no data set was written to the volume) a volume selected by the CTTGVL utility remains with a status of In-Use for three days, the status is removed by the CTTRTM retention management utility, which is normally run as part of the Control-M/Tape New Day procedure.
To select the appropriate volume, the CTTGVL utility scans the Control-M/Tape rules (according to supplied parameters) so that the volume that is returned is allocated from the appropriate pool.
The utility can optionally activate the Control-M/Tape Stacking facility that searches the Media database to locate a volume that has enough free space to hold the new file. Upon user request, or if such a volume cannot be located, a scratch volume can be returned instead.
The CTTGVL utility uses the active Control-M/Tape environment (in ECSA). Therefore, the utility can be called only on a CPU on that the Control-M/Tape environment is initialized.
If the CTTGVL utility is run simultaneously on more than one CPU, an enqueue manager, such as GRS, must be used to ensure that no volume is selected more than once by the utility.
The utility requires APF authorization. Therefore, it must reside in an authorized library and the load module that contains it (if linked to the user program) must also be authorized (parameter AC must be set to 1).
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