linux-ext4 - Re: [patch] ext2/3: document conditions when reliable operation is possible

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Message-ID: <87f94c370908241411r45079c5cx3fc737cf4c3f7d1e@mail.gmail.com>
Date:	Mon, 24 Aug 2009 17:11:56 -0400
From:	Greg Freemyer <greg.freemyer@...il.com>
To:	Pavel Machek <pavel@....cz>
Cc:	Ric Wheeler <rwheeler@...hat.com>, Theodore Tso <tytso@....edu>,
	Florian Weimer <fweimer@....de>,
	Goswin von Brederlow <goswin-v-b@....de>,
	Rob Landley <rob@...dley.net>,
	kernel list <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...l.org>, mtk.manpages@...il.com,
	rdunlap@...otime.net, linux-doc@...r.kernel.org,
	linux-ext4@...r.kernel.org
Subject: Re: [patch] ext2/3: document conditions when reliable operation is 
	possible

> The papers show failures in "once a year" range. I have "twice a
> minute" failure scenario with flashdisks.
>
> Not sure how often "degraded raid5 breaks ext3 atomicity" would bite,
> but I bet it would be on "once a day" scale.
>

I agree it should be documented, but the ext3 atomicity issue is only
an issue on unexpected shutdown while the array is degraded.  I surely
hope most people running raid5 are not seeing that level of unexpected
shutdown, let along in a degraded array,

If they are, the atomicity issue pretty strongly says they should not
be using raid5 in that environment.  At least not for any filesystem I
know.  Having writes to LBA n corrupt LBA n+128 as an example is
pretty hard to design around from a fs perspective.

Greg
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