I've looked at this a bit and even ran some numbers.  Here's what I've
determined.

When you first define the pool, devclass, etc., and assign a max scratch
value, the first time ADSM mounts a tape, it determines the native capacity
of the cartridge and multiplies by maxscratch to provide the estimated
capacity number.  So for DLT4000, you get 20GB times maxscratch.  The
estimated capacity for this pool will stay at this number until a cartridge
exceeds the 20 GB native capacity.  It will then grow, based on the
following: average the capacity consumed by each tape including the volumes
represented by maxscratch but not actually used and multiply by maxscratch.
So if you have 10 DLT4000 tapes at 20 GB each, you will have an estimated
capacity of 200 GB for the pool.  Say a tape then has 30 GB of stuff stored
on it.  The average capacity for the 10 tapes is 21 GB, so the estimated
capacity jumps to 210 GB.

ADSM knows how much data is saved on each tape.  What it can't possibly know
is how much tape is left on the real!

Kelly J. Lipp
Storage Solutions Specialists, Inc.
PO Box 51313
Colorado Springs CO 80949
719-531-5926
www.storsol.com
lipp AT storsol DOT com