One thing I have seen every now and then, is when a large file spans
multi-volumes, it will only get reported in utilization on one of the tapes,
but when query the contents of volumes, it will show up as on both.

David N. Reiss
TSM Support Engineer
david.reiss AT swpc.siemens DOT com
407-736-3912


-----Original Message-----
From: Price, Bob R. [mailto:bob.price AT MARCONI DOT COM]
Sent: Wednesday, September 25, 2002 10:45 AM
To: ADSM-L AT VM.MARIST DOT EDU
Subject: Under-utilized tape volumes


Can anyone share some understanding of the follow issue?

I have several tapes that appear to be grossly under-utilized.  Tapes marked
FULL (and even 100% utilized) that have 50GB-60GB capacity figures on a
100GB AIT3 cartridge.  Most full tapes show 90-110GB and a few where
compression is good shows up to 400GB.

My concern is with the 50-60GB ones.  What can cause such behavior?  I have
a few theories, but cannot pin anything down definitively.

My  theories:
1) On backups that are directed to skip the disk pool and write directly to
tape, changing files that are retried do not reposition the tape, but
instead continue writing causing large amounts of "unused" tape.  This
explains primary tape pools, but not copy pool tapes which show similar
under-utilized values.
2) Again, on backups that are directed to skip the disk pool and write
directly to tape, stopped tape motion could conceivably cause tape area to
be skipped on tape motion start-up.  I really have no evidence if this
actually occurs, but it is a thought.
3) File meta-data is written to tape and not the TSM database along with the
file data and is not reported in the capacity figure.  I can almost belive
that this could take up 50% of the space on selected clients.


Any comments on the above theories, especially arguments why they cannot be
true are welcome.  As are those comments expousing new theories or known
facts.

Bob Price
TSM / ADSM Administrator
Marconi Services
(412) 374-3247
WIN 284-3247
Fax: (412) 374-6371
Email: Bob.Price AT Marconi DOT com