From: Eric Sandeen Subject: Re: What happened to data=guarded? Date: Tue, 11 Aug 2009 13:04:50 -0500 Message-ID: <4A81B2C2.3040301@redhat.com> References: <1249934623-15939-1-git-send-email-tytso@mit.edu> <200908111535.37927.elendil@planet.nl> <20090811133721.GD29224@think> <200908111654.38217.elendil@planet.nl> <878whqgyid.fsf@basil.nowhere.org> <20090811153425.GB26070@atrey.karlin.mff.cuni.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: Andi Kleen , Frans Pop , Chris Mason , "Theodore Ts'o" , linux-kernel@vger.kernel.org, linux-ext4@vger.kernel.org To: Jan Kara Return-path: Received: from mx2.redhat.com ([66.187.237.31]:34489 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752350AbZHKSFJ (ORCPT ); Tue, 11 Aug 2009 14:05:09 -0400 In-Reply-To: <20090811153425.GB26070@atrey.karlin.mff.cuni.cz> Sender: linux-ext4-owner@vger.kernel.org List-ID: Jan Kara wrote: >> Frans Pop 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. Yes, I think the people anxiously waiting for data=guarded may be sadly surprised at their 0-length files. For those who understand the data=writeback tradeoffs it'll be very useful in terms of more consistent results (easily-detectable 0-size or short files, vs. randomly corrupted data sprinkled around) but it's not going to be "data=ordered, but faster!" -Eric > Honza