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

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Date:	Wed, 10 Nov 2010 15:27:21 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Pavel Machek <pavel@....cz>
Cc:	Dave Chinner <david@...morbit.com>,
	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>,
	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


* Pavel Machek <pavel@....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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