From: Jan Kara Subject: Re: Ext3 behavior on power failure Date: Wed, 28 Mar 2007 15:29:04 +0200 Message-ID: <20070328132903.GI14935@atrey.karlin.mff.cuni.cz> References: <4603B03E.7080302@emc.com> <20070328124015.GG14935@atrey.karlin.mff.cuni.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Ric Wheeler , armangau_philippe@emc.com, ext3-users@redhat.com, linux-ext4@vger.kernel.org, csar@stanford.edu To: "John Anthony Kazos Jr." Return-path: Received: from atrey.karlin.mff.cuni.cz ([195.113.31.123]:40059 "EHLO atrey.karlin.mff.cuni.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751564AbXC1N3E (ORCPT ); Wed, 28 Mar 2007 09:29:04 -0400 Content-Disposition: inline In-Reply-To: Sender: linux-ext4-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org > > If you fsync() your data, you are guaranteed that also your data are > >safely on disk when fsync returns. So what is the question here? > Pardon a newbie's intrusion, but I do know this isn't true. There is a > window of possible loss because of the multitude of layers of caching, > especially within the drive itself. Unless there is a super_duper_fsync() > that is able to actually poll the hardware and get a confirmation that the > internal buffers are purged? OK :), to correct myself: After fsync() returns, all the data is acked from the disk (or at least it should be like that unless there's a bug somewhere). So if there are some caches in the hardware which the hardware is not able to flush on power failure, that's a bad luck... That's why you should turn off write caching on cheaper disks if you really care about data integrity. Honza -- Jan Kara SuSE CR Labs