linux-ext4 - Re: What happened to data=guarded?

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Message-ID: <20090811153425.GB26070@atrey.karlin.mff.cuni.cz>
Date:	Tue, 11 Aug 2009 17:34:25 +0200
From:	Jan Kara <jack@...e.cz>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Frans Pop <elendil@...net.nl>,
	Chris Mason <chris.mason@...cle.com>,
	Theodore Ts'o <tytso@....edu>, jack@...e.cz,
	linux-kernel@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: What happened to data=guarded?

> Frans Pop <elendil@...net.nl> writes:
> 
> > On Tuesday 11 August 2009, Chris Mason wrote:
> >> On Tue, Aug 11, 2009 at 03:35:36PM +0200, Frans Pop wrote:
> >> > Somewhat unrelated, but what happened to the data=guarded patches
> >> > Chris Mason proposed back in April?
> >>
> >> I missed 2.6.31 but plan on sending for 2.6.32.  I promised to send
> >> along a forward port of the patches a while back, but I finally have
> >> one in testing here.  It should go out shortly.
> >
> > Good to hear. I've so far stayed with data=ordered as I think I'd prefer 
> > data=guarded over data=writeback. I'll certainly give it a try when it's 
> > available.
> 
> Same here. data=writeback already cost me a few files after crashes here :/
  In this regard, data=guarded need not be better than data=writeback.
We push out the data in guarded mode as late as in writeback mode
(that's where the performance benefit comes from ;). The difference is
that we increase i_size only after data are safely on disk so we cannot
expose old data.
  So security-wise, guarded mode is as safe as ordered mode but in other
aspects its more like data=writeback.

								Honza
-- 
Jan Kara <jack@...e.cz>
SuSE CR Labs
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