Since it's impossible to tell how much info a tape can hold, ADSM does the
following:

Up until it reaches the 10 GB, it assumes it's going to hold 10 GB.  Once 10
GB has been stored on the tape, then the estimated capacity actually states
how much data is on the tape.  Once the tape is full, estimated capacity is
the amount of data stored on the tape.  As files expire, pct utilized *
estimated capacity yields the actual amount of data on the tape.

Another interesting side effect of this is the estimated capacity of a pool.
This is determined as follows:

With just a little data on one tape, not enough to get to the rated tape
capacity, pool est capacity is maxscratch * the rated capacity.  So for a
pool with 20 scratch and 10 GB per tape, you get 200 GB as the estimated
capacity.  Then, as a tape goes beyond the rated capacity, the pool estimate
will go up.  I calculated how at one point, but my memory is fuzzy.  I
believe the algorithm takes an average of the tape estimated capacity *
maxscratch.

This is all fairly nebulous as one never knows how compressible data might
be.  I'm sure one of our resident SQL gurus will provide us a query that
will yield the exact capacity.

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