linux-kernel - Re: 2.6.36 io bring the system to its knees

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Date:	Wed, 10 Nov 2010 19:24:58 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Evgeniy Ivanov <lolkaantimat@...il.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jens Axboe <axboe@...nel.dk>, dave b <db.pub.mail@...il.com>,
	Sanjoy Mahajan <sanjoy@...n.edu>,
	Jesper Juhl <jj@...osbits.net>,
	Chris Mason <chris.mason@...cle.com>,
	Ingo Molnar <mingo@...e.hu>, Pekka Enberg <penberg@...nel.org>,
	Aidar Kultayev <the.aidar@...il.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Nick Piggin <npiggin@...e.de>,
	Arjan van de Ven <arjan@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>, Ted Ts'o <tytso@....edu>,
	Corrado Zoccolo <czoccolo@...il.com>,
	Shaohua Li <shaohua.li@...el.com>,
	Steven Barrett <damentz@...il.com>
Subject: Re: 2.6.36 io bring the system to its knees

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@...morbit.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@...morbit.com
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