Re: SCSI tape access on 2.6 kernels?

Kai Makisara
2006-01-25T21:24:35Z

On Tue, 24 Jan 2006, Kai Makisara wrote:

...
> One thing that can affect your comparisons is that the amount of data is
> quite small compared to the drive speed. The startup delay may be a
> significant factor in the timings (it differs depending on where the tape
> is and what has happened before the test). Even taking this into account,
> the speeds you see with 2.6 are too small.
>
I think I said this too weakly ;-) If you want to measure the streaming
speed of the tape system, the test file must be large enough. It can take
tens of seconds before a streamer starts writing and this time does vary
depending on the tape position, tape, has the drive been reading/writing
before, etc. You can verify this i you can listen what the drive is doing
during the tests. You can also try writing very small files and measure
the times.

A rule of thumb might be to have a test data that takes one or more
minutes to read/write. The HP LTO-3 raw speed is 80 MB/s without
compression. So, for a one minute test you should have 800 MB of
uncompressible data (or switch compression off).

--
Kai