PowerVault 100T, enabling compression

[Peter Bakker]

We have a PE2850 with PowerVault 100T SCSI tape backup unit with CentOS 
5 64-bit installed. Using tar and mt we are trying to modify a backup 
script which will enable hardware compression. Version of mt is mt-st v. 
0.9b.

Command "mt -f /dev/nst0 status" gives output:

SCSI 2 tape drive:
File number=0, block number=0, partition=0.
Tape block size 512 bytes. Density code 0x47 (TR-5).
Soft error count since last status=0
General status bits on (41010000):
 BOT ONLINE IM_REP_EN

There is no indication of compression status. I find I can issue command 
"mt -f /dev/nst0 compression on", but there is no feedback to indicate 
anything has changed.

An older PE2550 with GNU mt version 2.4.2 allowed use of command "mt -f 
/dev/nst0 datcompression 2" where 0=off, 1=show status, 2=on.

Does anyone know how to control hardware compression on the PowerVault 
100T? A pointer would be appreciated. Alternatively we could use 
compression at the application level, but hardware compression has 
worked well in the past.