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Date: Wed, 10 Nov 2010 15:27:21 +0100
From: Ingo Molnar <mingo@elte.hu>
Subject: Re: 2.6.36 io bring the system to its knees
Message-ID: <20101110142721.GA14496@elte.hu>
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To: Pavel Machek <pavel@ucw.cz>
Cc: Dave Chinner <david@fromorbit.com>, Linus Torvalds <torvalds@linux-foundation.org>, Jens Axboe <axboe@kernel.dk>, dave b <db.pub.mail@gmail.com>, Sanjoy Mahajan <sanjoy@olin.edu>, Jesper Juhl <jj@chaosbits.net>, Chris Mason <chris.mason@oracle.com>, Pekka Enberg <penberg@kernel.org>, Aidar Kultayev <the.aidar@gmail.com>, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>, Peter Zijlstra <a.p.zijlstra@chello.nl>, Nick Piggin <npiggin@suse.de>, Arjan van de Ven <arjan@infradead.org>, Thomas Gleixner <tglx@linutronix.de>, Ted Ts'o <tytso@mit.edu>, Corrado Zoccolo <czoccolo@gmail.com>, Shaohua Li <shaohua.li@intel.com>, Steven Barrett <damentz@gmail.com>
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* Pavel Machek <pavel@ucw.cz> wrote:

> Hi!
> 
> > > > As already mentioned, ext3 is just not a good choice for this sort of
> > > > thing. Did you have atimes enabled?
> > > 
> > > At least for ext3, more important than atimes is the "data=writeback"
> > > setting. Especially since our atime default is sane these days (ie if
> > > you don't specify anything, we end up using 'relatime').
> > > 
> > > If you compile your own kernel, answer "N" to the question
> > > 
> > >   Default to 'data=ordered' in ext3?
> > > 
> > > at config time (CONFIG_EXT3_DEFAULTS_TO_ORDERED), or you can make sure
> > > "data=writeback" is in the fstab (but I don't think everything honors
> > > it for the root filesystem).
> > 
> > Don't forget to mention data=writeback is not the default because if your system 
> > crashes or you lose power running in this mode it will *CORRUPT YOUR FILESYSTEM* 
> > and you *WILL LOSE DATA*. Not to mention
> 
> You will lose your data, but the filesystem should still be consistent, right? 
> Metadata are still journaled.

That is data that was freshly touched around the time the system went down, right?

I.e. data that was probably half-modified by user-space to begin with.

	Ingo

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