Jon LaBadie wrote:

On Thu, Jun 19, 2003 at 03:21:12PM +0100, Tom Brown wrote:

define tapetype unknown-tapetype {
   comment "just produced by tapetype prog (hardware compression on)"
   length 100608 mbytes

Wow!!!

   filemark 0 kbytes
   speed 12899 kps
}

...

Is the comment correct, was HW compression ON?  Should not have been.
A tapetype report should show the "native" capacity.

There was a significant (> 20%) difference in writing speed when
writing very compressable data and uncompressable data.
(45 seconds vs 77 seconds for 1 Gbyte).  This is a strong
indication for having hardware compression on.  That is because
(in the drives I have experience with) the writing of the bits
to tape is the limiting speed factor (unless your computer
cannot feed the bytes fast enough).

However, the hardware compression algorithm seems to be a very
good one: the measured capacity is still about 100 GByte.
This means that the algorithm does not fall into the known pitfall
of blindly imposing it's compression engine to an uncompressable
data stream.  (gnuzip does this too, compress does not.)

If this is really the case, then, maybe it's not necessary
to disable hardware compression at all.  And maybe, there isn't
even a possibility to do it (just as there is no setting to
tune your error correcting bits).

--
Paul