PowerVault 100T tape backup, hardware compression

[Peter Bakker]

Some further work was done with our 100T DAT72 tape backup unit to get 
it to use hardware compression.

Today I used the Dell Tape Diagnostic Utility from the CD supplied with 
the unit to do the compression test. The test is described as confirming 
that hardware data compression is operational on the drive.

    [root at xxxx Linux]# ./TapeRx.lx ctest -id:0
    Fri Feb  6 15:56:49 2009
    SCSI Port: 1, Bus: 0, Target: 6, Lun: 0
    DELL PV-100T-DAT72, Firmware: A060-052
    Serial# HV05G4R

    Issued Cmd: Test Compression.
    Examining compression attributes.
    Issued Cmd: Test Unit Ready.
    Issued Cmd: Load Tape.
    Issued Cmd: Write 20 MB to tape.
    Write Command Complete.
    Issued Cmd: Write File Marks.
    Issued Cmd: Rewind Tape.
    Issued Cmd: Read 20 MB from tape.
    Tape drive compression is operating normally.
    Issued Final Cmd: Rewind Tape.

The test was done withCentOS 5.2 64-bit, with no apparent issues.

The jumper switch settings on the bottom of the tape drive were checked 
and both switches 1 and 2 which arelate to data compression are in the 
default ON position. I also tried the same diagnostic test with switch 2 
in the OFF position, and obtained the following response from the TapeRx 
test (after a reboot so that the switch position would be read):

    [root at xxxx Linux]# ./TapeRx.lx ctest -id:0
    Fri Feb  6 15:29:32 2009
    SCSI Port: 1, Bus: 0, Target: 6, Lun: 0
    DELL PV-100T-DAT72, Firmware: A060-052
    Serial# HV05G4R

    Issued Cmd: Test Compression.
    Examining compression attributes.
    Unable to begin the test; device compression is turned off.

I would like to be able to control hardware compression from the command 
line using the mt (magnetic tape) utility but have been unsuccessful in 
using it to enable hardware compression. There is no indication of 
compression status using "mt -f /dev/nst0 status". I find I can issue 
command
    mt -f /dev/nst0 compression on
but there is no feedback to indicate anything has changed. Uncompressed 
the DAT72 tape holds 36G.

If anyone knows how to issue the SCSI command to get the 100T to use 
hardware data compression that would be appreciated.
Output from /proc/scsi/scsi shows the tape drive as follows:

    Host: scsi1 Channel: 00 Id: 06 Lun: 00
      Vendor: SEAGATE  Model: DAT    DAT72-052 Rev: A060
      Type:   Sequential-Access                ANSI SCSI revision: 03


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