I'm no IBM'er but a few cents on VTS:

VTS is nothing else than a RS6K with ADSM, disk pools and tape pools. Virtual
tapes are real files in a filesystem managed by hsm. To append a virtual tape, 
the
vts has to recall the old "tape" file and to append it. If VTS uses 10 GB 
virtual
volumes it has to recall a 10 GB file! If it has not enough space for recalling,
it has to empty the filesystem with migrating the existing volumes in advance of
recalling.

Maybe You should think about marking the tapes "readonly" after writing them the
first time? So You don't have as much recalls.

Using VTS for ADSM means knowing what You do. If  Your adsm floods Your vts disk
pool I would expect serious performance problems.

Roger Hohmann


Thomas Denier schrieb:

> 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?

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Roger Hohmann
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