From: Ric Wheeler <rwheeler@redhat.com>
Subject: Re: [patch] ext2/3: document conditions when reliable operation is
 possible
Date: Tue, 25 Aug 2009 20:11:21 -0400
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Cc: Theodore Tso <tytso@mit.edu>, Florian Weimer <fweimer@bfk.de>,
	Goswin von Brederlow <goswin-v-b@web.de>,
	Rob Landley <rob@landley.net>,
	kernel list <linux-kernel@vger.kernel.org>,
	Andrew Morton <akpm@osdl.org>, mtk.manpages@gmail.com,
	rdunlap@xenotime.net, linux-doc@vger.kernel.org,
	linux-ext4@vger.kernel.org, corbet@lwn.net
To: Pavel Machek <pavel@ucw.cz>
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On 08/25/2009 07:53 PM, Pavel Machek wrote:
>> Why don't you hold all of your most precious data on that single S-ATA
>> drive for five year on one box and put a second copy on a small RAID5
>> with ext3 for the same period?
>>
>> Repeat experiment until you get up to something like google scale or the
>> other papers on failures in national labs in the US and then we can have
>> an informed discussion.
>
> I'm not interested in discussing statistics with you. I'd rather discuss
> fsync() and storage design issues.
>
> ext3 is designed to work on single SATA disks, and it is not designed
> to work on flash cards/degraded MD RAID5s, as Ted acknowledged.

You are simply incorrect, Ted did not say that ext3 does not work with MD raid5.

>
> Because that fact is non obvious to the users, I'd like to see it
> documented, and now have nice short writeup from Ted.
>
> If you want to argue that ext3/MD RAID5/no UPS combination is still
> less likely to fail than single SATA disk given part fail
> probabilities, go ahead and present nice statistics. Its just that I'm
> not interested in them.
> 									Pavel
>

That is a proven fact and a well published one. If you choose to ignore 
published work (and common sense) that RAID makes you lose data less than 
non-RAID, why should anyone care what you write?

Ric