On Jan 16, 2006, at 12:14 PM, Prather, Wanda wrote:

...IF you have compression turned on at your TSM client, the data is
already compressed, and the tape drive probably won't be able to
compress it any more.  In fact, there are SOME cases where the data
can
grow a bit if it is compressed a second time.  But if you have a
mix of
ordinary AIX and Windows servers, that is generally not enough of an
issue to worry about.

Modern tape drive technology can be quite sophisticated about
compression.
The 3592 SCSI Reference manual says:

"The TotalStorage 3592 uses an optimal dynamic compression method
called byte level compression scheme swapping. This insures that the
maximum data compressability is always achieved, and unlike other
tape drive compression methods, the data will never expand."

  Richard Sims