linux-kernel - Re: [testcase] test your fs/storage stack (was Re: [patch] ext2/3: document conditions when reliable operation is possible)

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Message-ID: <20090903085510.GE3793@elf.ucw.cz>
Date:	Thu, 3 Sep 2009 10:55:10 +0200
From:	Pavel Machek <pavel@....cz>
To:	david@...g.hm
Cc:	Rob Landley <rob@...dley.net>, Ric Wheeler <rwheeler@...hat.com>,
	Theodore Tso <tytso@....edu>, Florian Weimer <fweimer@....de>,
	Goswin von Brederlow <goswin-v-b@....de>,
	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, corbet@....net
Subject: Re: [testcase] test your fs/storage stack (was Re: [patch] ext2/3:
	document conditions when reliable operation is possible)

Hi!

>> However, thinking about how to _fix_ a problem is predicated on acknowledging
>> that there actually _is_ a problem.  "The hardware is not physically damaged
>> but your data was lost" sounds to me like a software problem, and thus
>> something software could at least _attempt_ to address.  "There's millions of
>> 'em, Linux can't cope" doesn't seem like a useful approach.
>
> no other OS avoids this problem either.
>
> I actually don't see how you can do this from userspace, because when you 
> write to the device you have _no_ idea where on the device your data will 
> actually land.

It certainly is not easy. Self-correcting codes could probably be
used, but that would be very special, very slow, and very
non-standard. (Basically... we could design filesystem so that it
would survive damage of arbitrarily 512K on disk -- using
self-correcting codes in CD-like manner). I'm not sure if it would be
practical.

								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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