Joe,
        Move data will only move files on a tape volume that haven't expired.  
In
fact, when we were still running on an MVS system, I used the method Dwight
mentioned (move data volser stgpool=somediskstoragepool) instead of
reclamation because

1)      We had too many tapes in our tape storage pool (6,000+)
2)      At the time, reclamation was a single threaded process (think this has
since changed).
3)      I could generate a list of input tapes for our operators (no automated
tape library at the time) - this kept them happier and a little more
motivated to mount the tapes in a timely manner.
4)      I could run as many move data's at a time as I needed (usually 6-10).
5)      Control over what got moved and when (moved the least full tapes
first).

If you do a Q VOL volser F=D, you can figure out how much data is on a tape
based upon the estimated capacity, %Utl, Volume Status (filling or full),
etc.

Tim Pittson
tpittson AT himail.hcc DOT com