Managing alternate volumes

DFSMShsm provides full support for producing and managing one alternate tape for each volume in the categories of ML2 and backup tapes. As shown above, this includes using the duplex tape option, or using a generic TAPECOPY command to copy full tapes not already having a copy, and optionally interfacing to the DFSMShsm installation exit ARCTVEXT to return emptied tapes to scratch status.

Examples

Although it is possible for you to make multiple alternate tapes, that comes with the price of doing additional management of them, as detailed in the following two examples:

If you issue the TAPECOPY command to create an alternate tape for an original volume not marked full, then the original will likely be extended later.
When entries are being added to a base TTOC or when a tape is marked full for reasons other than a DELVOL MARKFULL command, any existing alternate volume is no longer valid. If, in either case, the tape already has an alternate volume, then message ARC0441I is issued to the console and appropriate activity log, and the existing alternate is removed. DFSMShsm does not take exit ARCTVEXT, unless it was a duplexed alternate, since it is not known whether the alternate tape should be returned to scratch status. If it was a duplexed alternate, DFSMShsm takes the ARCTVEXT installation exit, doesn't get rid of the alternate, and doesn't issue the ARC0441I message.
If you issue a specific TAPEREPL command specifying the alternate volume to replace the original tape, and the specified alternate is different from the alternate volume DFSMShsm knows about, then message ARC0439I is issued to the submitter and the command activity log. The alternate previously known to DFSMShsm is not retained. It is also not passed to the ARCTVEXT exit (although the original is) because DFSMShsm does not know whether you want it to be returned to scratch status.

For duplex tapes, after the original volume is replaced, it is marked full and is no longer a duplex tape.

The first example above is an instance where DFSMShsm directs a specific message to the console so that if automatic operations are desired, they can be implemented based on intercepting a console message.

If an ML2 or backup tape is deleted using the DELVOL command, DELVOL processing issues message ARC0420I for the alternate volume recorded by DFSMShsm.