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Date: Tue, 24 Dec 2002 10:18:52 +0100
Subject: Re: Horrible drive performance under concurrent i/o jobs (dlh problem?)
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Cc: "'David Lang'" <dlang@diginsite.com>,
       "'Torben Frey'" <kernel@mailsammler.de>, <linux-kernel@vger.kernel.org>
To: "Joseph D. Wagner" <wagnerjd@prodigy.net>
From: Roy Sigurd Karlsbakk <roy@karlsbakk.net>
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> SHORT ANSWER: Segregating partitions reduces seek time.  Period.
>
> LONG ANSWER: Reads and writes tend to be grouped within a partition.  
> For
> example, if you're starting a program, you're going to be doing a lot 
> of
> reads somewhere in the /usr partition.  If the program uses temporary 
> files,
> you're going to do a lot of reads & writes in the /tmp partition.  If 
> you're
> saving a file, you're going to be doing lots of writes to the /home
> partition.  Hence, since most disk accesses occur in groups within a
> partition, preference should be giving to reducing seek time WITHIN a
> partition, rather than reducing seek time BETWEEN partitions.

keep in mind that only around half of the seek time is because of the 
partition! Taking an IBM 120GXP as an example:

Average seek:				8.5ms
Full stroke seek:			15.0ms
Time to rotate disk one round:	1/(7200/60)*1000 = 8.3ms

Then, the sector you're looking for, will, by average, be half a round 
away from where you are, and thus, giving the minimum average seek time 
8.3/2 = 4.15ms or something like half the seek time. Concidering this, 
you may gain a maximum <= 50% gain in using smaller partitions.

btw. anyone that knows the zone layout on IBM drives?

roy

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