linux-kernel - Re: Abysmal disk performance, how to debug?

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Message-ID: <20070120203140.GE25307@1wt.eu>
Date:	Sat, 20 Jan 2007 21:31:41 +0100
From:	Willy Tarreau <w@....eu>
To:	Tim Schmielau <tim@...sik3.uni-rostock.de>
Cc:	Ismail Dönmez <ismail@...dus.org.tr>,
	linux-kernel@...r.kernel.org
Subject: Re: Abysmal disk performance, how to debug?

On Sat, Jan 20, 2007 at 09:28:57PM +0100, Tim Schmielau wrote:
> On Sat, 20 Jan 2007, Willy Tarreau wrote:
> 
> > Anyway, in your situation with a very small buffer, this should not 
> > change by more than half a second or so.
> 
> Well, his buffer is not small. He has half a GB of RAM, so when 
> writing 1 GB the buffer would roughly double the dd speed, exactly as he 
> has shown us.

yes, but he sees the opposite : when using half of the memory for the
buffer, he has low speed. When shorting cache size to 2% only, he doubles
his speed.

> Anyways, instead of always just posting similar answers to yours, I'll 
> have dinner now. :-)

:-)
Willy

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