How to use space more efficiently in a VTL

Answer

VTL and physical libraries are unaware of Tivoli Storage Managers expired data on tape/sequential media.

The reclamation process writes the remaining data from an existing tape/volume to a new volume but does not remove/delete the data from the source volume. The server changes the data reference to the new storage tape/volume.

With a physical library there is no intelligence to reference the data on the volume When a volume returns to scratch, Tivoli Storage Manager no longer has any data reference points on that volume and hence will write new data after the tape header effectively overwriting the already expired/reclaimed data.

The VTL, however, keeps track of the bit vectors which have data and just because Tivoli Storage Manager no longer references the data the VTL still does.
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Writing at the beginning of tape (BOT) frees space taken by the VTL cartridge/volume.

Tivoli storage Manager can be directed to rewrite the tape label immediately after the volume returns to scratch via the RELABELSCRatch parameter on the Define Library or Update Library command:

RELABELSCRatch=Yes