Date: Wed, 10 Nov 2010 19:24:58 +1100
From: Dave Chinner <david@fromorbit.com>
To: Evgeniy Ivanov <lolkaantimat@gmail.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
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On Wed, Nov 10, 2010 at 11:08:17AM +0300, Evgeniy Ivanov wrote:
> On Wed, Nov 10, 2010 at 4:32 AM, Dave Chinner <david@fromorbit.com> wrote:
> > 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
> > the significant security issues (e.g stale data exposure) that also
> > occur even if the filesystem is not corrupted by the crash. IOWs,
> > data=writeback is the "fast but I'll eat your data" option for ext3.
> >
> > So I recommend that nobody follows this path because it only leads
> > to worse trouble down the road. ?Your best bet it to migrate away
> > from ext3 to a filesystem that doesn't have such inherent ordering
> > problems like ext4 or XFS....
> 
> Is it save to use "data=writeback" with ext4?

I believe the same issues exist with data=writeback in ext4, but you
probably should have an ext4 developer answer that question for
certain.

> At least are there security issues?
> Why do you say, that fs can be corrupted? Metadata is still
> journalled, so only data might be corrupted, but FS should still be
> consistent.

Data corruption is still a filesystem corruption.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com
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