Date: Tue, 5 Mar 2002 18:54:04 -0500 From: Brian T.Schellenberger <bts@babbleon.org> To: Julian Elischer <julian@elischer.org>, Lars Eggert <larse@ISI.EDU> Cc: Zhihui Zhang <zzhang@cs.binghamton.edu>, "Rogier R. Mulhuijzen" <drwilco@drwilco.net>, freebsd-hackers@FreeBSD.ORG Subject: Re: A weird disk behaviour Message-ID: <20020305235404.9AE73BA03@i8k.babbleon.org> In-Reply-To: <Pine.BSF.4.21.0203051529100.26829-100000@InterJet.elischer.org> References: <Pine.BSF.4.21.0203051529100.26829-100000@InterJet.elischer.org>
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On Tuesday 05 March 2002 06:29 pm, Julian Elischer wrote:
> On Tue, 5 Mar 2002, Lars Eggert wrote:
> > Zhihui Zhang wrote:
> > > Several times slower! The point is that writing less data performs
> > > worse. So I call it weird.
> >
> > Huh? You originally said:
> > > (1) Write each block fully and sequentially, ie. 8192 bytes.
> > >
> > > (2) I still write these blocks sequentially, but for each block I only
> > > write part of it.
> >
> > ...
> >
> > > I find out the the performance of (2) is several times better than the
> > > performance of (1). Can anyone explain to me why this is the case?
> >
> > If (2) is better than (1), then writing *less* data is faster. Which is
> > it, now?
>
> Um yeah that is what all my suggestions were based on..
If, however, the later mail is right and the earlier mail is wrong, this
*would* be easily explained: Many disks have optimization for the case of
linear writes and seeking slows them down a *lot*. Why? Because it's very
common to do linear writes, and it make sense to optimize the common case.
But it'll be easier for us all to explain away the results if you can tell us
what the results actually are :-)
>
> > Lars
>
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