Look at the format of the device class for the drives.
If you let it default to "DRIVE" it will use all available hardware
compression...
I always tell clients to use compression and I also have the drives set to
use compression.

tsm: TSMSRV10>q dev f=d

             Device Class Name: 3590E1A
        Device Access Strategy: Sequential
            Storage Pool Count: 6
                   Device Type: 3590
                        Format: DRIVE
                                <stuff deleted>


Syntax

>>-DEFine DEVclass--device_class_name----DEVType--=--3590------->

      .-FORMAT--=--DRIVE-------.
>-----+------------------------+--LIBRary--=--library_name------>
      '-FORMAT--=--+-DRIVE---+-'
                   +-3590B---+
                   +-3590C---+
                   +-3590E-B-+
                   '-3590E-C-'
        <stuff deleted>
FORMAT
     Specifies the recording format to be used when writing data to
     sequential access media. This parameter is optional; the default value
     is DRIVE.

     The following are possible values for 3590 devices:

     DRIVE
          Specifies that TSM selects the highest format that can be
          supported by the sequential access drive on which a volume is
          mounted.

     3590B
          Specifies that TSM writes data using the basic (uncompressed)
          format. This results in a tape capacity of approximately 10GB.

     3590C
          Specifies that TSM writes data using the compressed format. This
          results in a tape capacity of approximately 10GB. However, this
          format uses the tape drive's hardware compression feature so the
          actual capacity may be greater depending on the effectiveness of
          compression.

     3590E-B
          Specifies that TSM writes data by using the uncompressed format
          similar to the 3590B format. This results in a tape capacity of
          approximately 10GB.

     3590E-C
          Specifies that TSM writes data by using the compressed format
          similar to the 3590C format. This results in a tape capacity of
          approximately 10GB. However, this format uses the tape drive's
          hardware compression feature so the actual capacity may be greater
          depending on the effectiveness of compression.