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Date: Wed, 26 Jan 2005 20:04:18 -0800 (PST)
From: Arne "W�rner" <arne_woerner@yahoo.com>
To: delphij@delphij.net
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cc: freebsd-fs@FreeBSD.ORG
Subject: Re: ufs+softupdates / consistency
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--- Xin LI <delphij@frontfree.net> wrote:
> 在 2005-01-26三的 17:42 -0800，Arne WXrner写道：
> > Can somebody explain me, why write speed is so much slower
> > than read speed (even with hard disc write cache)?
> 
> This is common case caused by physical constraints I guess :-)

> > I tried an UFS1 file system mounted async for another test.
> > And the write speed was still about 5 Mbyte/sec.
> 
> Well, I haven't benchmarked it by myself, however, the author of
> SoftUpdates claims that the benchmark should be 95% or so as you
> async mount a UFS file system.  BTW: I think 5MB/s of write
> speed is somewhat too slow for an IDE device, you may want to
> check the cable, etc.
>
Hmm. I tried a "dd if=/dev/zero of=a bs=64k count=1000 ; sync"
with KNOPPIX and the same slice/cable and ext3fs (mkfs with
defaults) and it was about 4 times faster than FreeBSD R5.3.

Furthermore the read speed is about 25Mbyte/sec, so that the cable
seems to be ok.

Funnily my other hard disc (SAMSUNG SP1604N), which uses the same
cable, is much faster:
 write
  (bs=64k count=1000 if=/dev/zero):
  appr. 48Mbyte/sec
 read
  (bs=64k count=3975 if=<another file>):
  appr. 38Mbyte/sec (???????????)
I do not understand this different behaviour... *sniff*

-Arne



		
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