On Sun, Sep 22, 2002 at 10:44:35AM +0200, Martin Schwarz wrote:
> On Sat, Sep 21, 2002 at 04:00:31PM -0400, Gene Heskett wrote:
> > The above looks as if you have the drives compression turned on, 
> 
> I have, although I should know better about this - having read the list
> for a while. Somehow I never thought about my own setup when reading
> about the cons of hardware compression... will switch it off.

Hardware compression is now switched off (both with the drive's internal
dip switch and the mt utility option), and I have rerun tapetype after
making sure the tape's internal information on this was cleared
(following Gene's instructions - thanks!). The results are as follows
(this is a WangDAT 3400DX SCSI DAT drive with a DDS2 120m tape):

----------------------------------------------------------------
martin@lissy:~$ sudo -u backup tapetype -h
usage: tapetype -h [-e estsize] [-f tapedev] [-t typename]
  -h                    display this message
  -e estsize            estimated tape size (default: 1g == 1024m)
  -f tapedev            tape device name (default: $TAPE)
  -t typename           tapetype name (default: unknown-tapetype)

Note: disable hardware compression when running this program.
martin@lissy:~$ time sudo -u backup tapetype -e 4g -t DDS2-120m && echo
done.
wrote 121830 32Kb blocks in 93 files in 11355 seconds (short write)
wrote 111350 32Kb blocks in 170 files in 11570 seconds (short write)
define tapetype DDS2-120m {
    comment "just produced by tapetype program"
    length 4202 mbytes
    filemark 4355 kbytes
    speed 325 kps
}

real    384m37.786s
user    0m1.980s
sys     4m6.670s
done.
martin@lissy:~$
----------------------------------------------------------------

I'm not sure if this is correct.

- The length value looks good. How was that influenced by the estimate
  of 4GByte I gave with the -e option? I had left out this option the
  last time I ran tapetype. 
- The filemark seems to be unusually high. Can this be correct? Does
  this mean I'm wasting over 4 MBytes between two files on tape? Is this
  something that can be changed or is it a property of the drive?
- The speed is not that high, but might well be correct. The machine the
  tape drive is connected to is a lowly Pentium-133...

I will try to rerun the tapetype utility on another tape and see if the
results are similar.

Thanks for your time and your comments!
Martin.