My site is planning to install an ADSM Version 3 server on an MVS system. We
are also planning to install a 3494 automatic tape library with a VTS (Virtual
Tape Server). Current plans call for sending incoming backup data to primary
tape storage pools using the VTS. The disk cache on the VTS is almost
certainly large enough to keep new backup data on disk until a COPY STGPOOL is
done to produce off-site backups, and probably large enough to keep partially
filled virtual tapes on disk until ADSM puts more data on them.

I am a bit nervous about the amount of behind the scenes tape activity this
approach will entail. Each time ADSM adds data to a partially filled virtual
volume, the real tape space occupied by the old version of the virtual volume
will go out of use. I would expect this to end up triggering large amounts of
VTS tape reclamation activity. I am also nervous about the two-tiered
reclamation we will be doing as ADSM clears virtual volumes and the VTS
eventually clears the real volumes formerly occupied by the reclaimed virtual
volumes.

What are the pros and cons of using a VTS for ADSM primary storage pools?