My site is using an IBM 3494 tape library with a VTS (Virtual Tape Server) to
store ADSM data.

Most specific volume mounts of virtual tapes for ADSM take about five minutes.
I understand that the process is more complicated than mounting a real tape,
but even so, five minutes does not seem an impressive performance for what is
advertized as a highly advanced tape technology.

I have occasionally seen virtual tape mounts for ADSM take forty minutes or
more with no obvious cause. The people who manage the VTS insist that these
episodes are normal behavior (they usually say something about the length of
time required to forward space a ten gigabyte stacked volume). I find this
claim implausible in the extreme, but I don't know how to refute it.

Are there any IBM documents with concrete data on the expected mount times for
virtual tapes?