We just installed IDRC capability on our 3480 tape drives.  On VM, the
compression is normally not used unless specifically requested and most
of the products we run do the same.  However, our astute Operations Manager
noticed a potential problem for us in ADSM.  Our CARTRIDGE device class
is defined as FORMAT=DEVICE.  This is the default.  The description of this
says that ADSM will use the highest format that the drive is capable of
using.  Does this mean that, now that we have IDRC installed, compression
will happen automatically?  What will that do to our current tape pool,
all of which was written without compression?  Should I change this
option to 3480 to avoid problems?  If so, then how do I get ADSM to use
compression without trashing my current tape pool?  (I suspect I know the
answer to the last one, but am hoping for the best anyway.)

Martha