One of my users has a special project to backup 800 Gb for a few days and
then throw it away.  Since we've just cleaned the test machine to put up
V4R2, I agreed and let him have the test machine for 3-4 days.  The machine
is configured just like production, in particular the DEVC=TAPE:

       Device Class Name: TAPE
  Device Access Strategy: Sequential
      Storage Pool Count: 7
             Device Type: 3590
                  Format: DRIVE
   Est/Max Capacity (MB):
             Mount Limit: DRIVES
        Mount Wait (min): 60
   Mount Retention (min): 2
            Label Prefix: ADSM
                 Library: TSMLIB

The drive is a 3590-E, which experience shows will hold 50-100 Gb,
depending on compression.  I put 30 new cartridges into the 3494, whcih
should have sufficed him with room to spare.

However, what I'm seeing consistently is a tape being marked full at
18.5-18.8 Gb.  It appears that all the files are pretty much the same size,
and there are lots of them.  But what can I do to get more onto a volume???