Continual mounting of data set backup tapes is possible because the MAXIDLETASKS parameter specifies the tapes be continuously mounted, or because the data set backup workload keeps a tape continuously mounted. Installations can use the SWITCHTAPES function to demount those tapes and deallocate those drives in preparation for disaster backup or the introduction of new tape devices.

The SWITCHTAPES function provides the ability both to plan for the switching of tapes using the DEFINE command or switch tapes as needed for unplanned events by using the HOLD command.

The DEFINE SWITCHTAPES command and its subparameters allow installations to define a time for performance of automatic demounting of data set backup tapes. This automatic demounting of tapes and the deallocation of the tape drives occurs either at a certain time of day or at the end of autobackup. After the tapes are demounted and the drives are deallocated, the data set backup tasks continue with newly selected tapes.

The PARTIALTAPE subparameter of the DEFINE SWITCHTAPES command is used to specify the method that DFSMShsm uses to mark a data set backup output tape as full. PARTIALTAPE(MARKFULL) specifies that all partial tapes demounted with the SWITCHTAPES option are to be marked full. PARTIALTAPE(REUSE) specifies that all partial tapes demounted with the SWITCHTAPES remain in the DFSMShsm inventory as partial tapes. PARTIALTAPE(SETSYS) specifies use of the SETSYS PARTIALTAPE value. PARTIALTAPE(MARKFULL) is the default.

The HOLD BACKUP(DSCOMMAND(SWITCHTAPES)) option demounts the mounted volumes, and if specified, causes the tapes to be marked full. Any other partial tapes in the DFSMShsm backup inventory remain as selection candidates as partial tapes and may be immediately selected and mounted for output processing. A subsequent RELEASE command is not necessary.

The partial tape status (REUSE or MARKFULL) is taken from the DEFINE SWITCHTAPES command.

After the tapes are demounted and the drives are deallocated, the data set backup tasks continue with newly selected tapes.

For more information about the specific command syntax and explanations of the commands and parameters affecting the SWITCHTAPES function, see z/OS DFSMShsm Storage Administration.