Re: ATA disk performance (ICH2 controller), some testsandcomparison with Linux 2.6.5

From: John-Mark Gurney <gurney_j_at_resnet.uoregon.edu>
Date: Sun, 26 Sep 2004 20:15:29 -0700
Mauro Triulzi wrote this message on Mon, Sep 27, 2004 at 02:20 +0200:
> ii) Now I tried a fair raw throughput comparison between Linux and 
>    FreeBSD. This time I read always the same whole (Linux) partition 
>    (~4GB) so that the results should be comparable. I always used native
>    dd (FreeBSD and Linux). A measure with Linux dd under emulation
>    in FreeBSD gave yet the same result:
> 
>    dd if=/dev/ad0s9 bs=nnn  of=/dev/null
>    FreeBSD:
> nnn=4k:   4301789184 bytes transferred in 170.031898 secs (25299895 
> bytes/sec)
> nnn=8k:   4301789184 bytes transferred in 114.446100 secs (37587905 
> bytes/sec)
> nnn=16k:  4301789184 bytes transferred in 87.794076 secs (48998627 
> bytes/sec)
> nnn=64k:  4301789184 bytes transferred in 89.515195 secs (48056525 
> bytes/sec)
> nnn=512k: 4301789184 bytes transferred in 90.357666 secs (47608458 
> bytes/sec)
>    (no significant changes before or after reinit)
> 
>    Linux:
> nnn=4k:   4301789184 bytes transferred in 93 secs (~46 Mbytes/sec)
> nnn=8k:   4301789184 bytes transferred in 86 secs (~50 Mbytes/sec)
> nnn=16k:  4301789184 bytes transferred in 90 secs (~48 Mbytes/sec)
> nnn=64k:  4301789184 bytes transferred in 95 secs (~45 Mbytes/sec)
> nnn=512k: 4301789184 bytes transferred in 92 secs (~47 Mbytes/sec)
> 
>    I notice, that the rates are very similar if bs >= 16k. Under FreeBSD 
>    the raw throughput rate depends on the block size. Read rate under Linux
>    is independent of the block size. Is there a special reason for that?

Last I heard Linux did not have a raw device.. this means that it will
always be cached, and will do various read-ahead optimizations, while
FreeBSD does not have a buffered/cooked device anymore..  w/o the cooked
device FreeBSD has to suffer the latency of the command to the drive...

-- 
  John-Mark Gurney				Voice: +1 415 225 5579

     "All that I will do, has been done, All that I have, has not."
Received on Mon Sep 27 2004 - 01:15:33 UTC

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