Date: Wed, 10 Nov 2010 15:20:37 +0100
From: Pavel Machek <pavel@ucw.cz>
To: Dave Chinner <david@fromorbit.com>
Cc: 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>, Ingo Molnar <mingo@elte.hu>,
        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>
Subject: Re: 2.6.36 io bring the system to its knees
Message-ID: <20101110142037.GA1447@ucw.cz>
References: <20101105014334.GF13830@dastard>
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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.

> the significant security issues (e.g stale data exposure) that also
> occur even if the filesystem is not corrupted by the crash. IOWs,

I agree on security issues.
									Pavel

-- 
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