Re: SCSI tape access on 2.6 kernels?

Gerhard Schneider
2006-01-24T21:01:13Z

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Kai Makisara schrieb:

> The only thing that could be seen in Gerhard's tests with try_direct_io=0
> should be higher CPU load. It probably won't have any effect on the speed
> in these tests.
>
> Disabling direct i/o helps in fixed block mode if the application's read()
> and write() byte counts are small, e.g., 10 kB. With 64 kB it should not
> have any effect. Additionally, Gerhard is probably using variable block
> mode and there is no read-ahead. There is write-behind which is disabled
> when doing direct i/o but this should have no effect since if the HBA is
> able to sustain the speed the drive requires.
>

I fear you're right. There hasn't been any significant difference in
write/read speed when enabling/disabling direct i/o (significant doesn't
mean a speedup of 20-100% - I want to see more than 40MB/s on a LTO-3
tape drive, and not 1.2)..

Different fixed and variable block sizes didn't show significant speed
increases, too.. - and I still expect a kernel problem, not a tape
problem..

Tomorrow I will compile a kernel < 2.6.12 and redo testing..

GS

--
Gerhard Schneider
Institute of Lightweight Design and e-Mail: gs@ilsb.tuwien.ac.at
Structural Biomechanics (E317) Tel.: +43 1 58801 31716
Vienna University of Technology / Austria Fax: +43 1 58801 31799
A-1040 Wien, Gusshausstrasse 27-29 http://www.ilsb.tuwien.ac.at/~gs/

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