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From: Kevin Grittner <Kevin.Grittner@wicourts.gov>
To: Gregory Stark <gsstark@mit.edu>
Cc: Matthew <matthew@flymine.org>
Cc: Mark Mielke <mark@mark.mielke.cc>
Cc: pgsql-performance@postgresql.org
Subject: Re: RAID arrays and performance
Date: Tue, 29 Jan 2008 11:13:54 -0600
Message-ID: <479F0A72.EE98.0025.0@wicourts.gov> (raw)
In-Reply-To: <873asginrz.fsf@stark.xeocode.com>
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	<873asginrz.fsf@stark.xeocode.com>

>>> On Tue, Jan 29, 2008 at 10:45 AM, in message
<873asginrz.fsf@stark.xeocode.com>, Gregory Stark <gsstark@mit.edu> wrote: 
 
> Well consider when you've reached n-1 drives; the expected number of requests
> before you hit the 1 idle drive remaining out of n would be n requests. When
> you're at n-2 the expected number of requests before you hit either of the 
> two
> idle drives would be n/2. And so on. The last term of n/n would be the first
> i/o when all the drives are idle and you obviously only need one i/o to hit 
> an
> idle drive.
 
You're right.  Perhaps the reason more requests continue to improve
performance is that a smart controller will move across the tracks
and satisfy the pending requests in the most efficient order?
 
-Kevin
 





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