Hi Listers,

Just to give my 0.02EUR

> > mt -f /dev/nst0 defcompression off (or 0 depending on your mt)
> > mt -f /dev/nst0 compression off (or 0 depending on your mt)

I am running SuSE 9.3 and the only available mt operation is
"datcompression"

See:
athene:~ # mt --version
GNU mt version 2.5
athene:~ # man mt
[...]
 datcompression
              (some  SCSI-2  DAT  tapes) Inquire or set the compression
status
              (on/off). If the count is one the compression status is
printed.
              If  the  count is zero, compression is disabled. Otherwise,
com-
              pression is enabled. The command uses the SCSI ioctl to read
and
              write  the Data Compression Characteristics mode page (15).
ONLY
              ROOT CAN USE THIS COMMAND.


And in fact I do have the problem that I use at one site the Tandberg SLR7
without knowing how to switch off hw-compression. The mt datcompression
{off|0} operation fails. That leads to my amanda.conf:

define tapetype SLR7 {
    comment "just produced by tapetype prog (hardware compression on)"
    length 16500 mbytes # Manually decreased again
    filemark 186 kbytes
    speed 1300 kps
}

athene:~ # dmesg | grep SLR
  Vendor: TANDBERG  Model: SLR7              Rev: 0483
  Type:   Sequential-Access                  ANSI SCSI revision: 02
Attached scsi tape st0 at scsi0, channel 0, id 3, lun 0
st0: try direct i/o: yes (alignment 512 B), max page reachable by HBA
1048575


BTW: Is it true that a tape formerly written with hw-compression will
"override" the 'drive compression off setting' because the compression
on/off status has been written on the header of the tape? If yes, I should
"reformat" a lot of tapes as described by Gene :-/


Best regards
Uwe


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