From: Ian Soboroff <isoboroff@acm.org>
To: Max Waterman <davidmaxwaterman@fastmail.co.uk>
Cc: linux-kernel@vger.kernel.org
Subject: Re: io performance...
References: <43CB4CC3.4030904@fastmail.co.uk> <43CD2405.4070902@cfl.rr.com>
	<43CDED23.5060701@fastmail.co.uk> <43CE5C7A.5060608@cfl.rr.com>
	<43D07C08.5000903@fastmail.co.uk> <9cfek33vwvo.fsf@nist.gov>
	<43D71C75.2050807@fastmail.co.uk>
Date: Wed, 25 Jan 2006 09:19:39 -0500
In-Reply-To: <43D71C75.2050807@fastmail.co.uk> (Max Waterman's message of
	"Wed, 25 Jan 2006 14:36:37 +0800")
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Max Waterman <davidmaxwaterman@fastmail.co.uk> writes:

>>> We're still wondering why rd performance is so low - seems to be the
>>> same as a single drive. RAID10 should be the same performance as RAID0
>>> over two drives, shouldn't it?
>>>
>> I think bonnie++ measures accesses to many small files (INN-like
>> simulation) and database accesses.  These are random accesses, which
>> is the worst access pattern for RAID.  Seek time in a RAID equals the
>> longest of all the drives in the RAID, rather than the average.  So
>> bonnie++ is domninated by your seek time.
>
> You think so? I had assumed when bonnie++'s output said 'sequential
> access' that it was the opposite of random, for example (raid0 on 5
> drives) :
>

I could be wrong, I was just reading the information from the bonnie++
website... 

Ian

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