From mboxrd@z Thu Jan 1 00:00:00 1970 From: Theodore Tso Subject: Re: Enable asynchronous commits by default patch revoked? Date: Mon, 24 Aug 2009 20:15:54 -0400 Message-ID: <20090825001554.GN17684@mit.edu> References: <200908241033.10527.Christian.Fischer@easterngraphics.com> <20090824133447.GH23677@mit.edu> <20090824183119.GI5931@webber.adilger.int> <20090824201027.GC17684@mit.edu> <4A92F7E0.9010001@redhat.com> <20090824220738.GG17684@mit.edu> <4A93103B.2000909@redhat.com> <20090824232804.GJ17684@mit.edu> <20090824234336.GU5931@webber.adilger.int> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Ric Wheeler , Christian Fischer , linux-ext4@vger.kernel.org To: Andreas Dilger Return-path: Received: from thunk.org ([69.25.196.29]:49455 "EHLO thunker.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753381AbZHYAP7 (ORCPT ); Mon, 24 Aug 2009 20:15:59 -0400 Content-Disposition: inline In-Reply-To: <20090824234336.GU5931@webber.adilger.int> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Mon, Aug 24, 2009 at 05:43:36PM -0600, Andreas Dilger wrote: > Without transaction checksums waiting on all of the blocks together > is NOT safe. If the commit record is on disk, but the rest of the > transaction's blocks are not then during replay it may cause garbage > to be written from the journal into the filesystem metadata. Yes, I *said* that we can only wait on all of the blocks together with the commit record when doing journal checksums. Sorry if I didn't make that clear enough. That's the one optimization we using journal checksums buys us. Unfortunately it does not allow us to omit the barrier operation.... and have real-world testing experience that without the barrier, a power drop can cause significant filesystem corruption and potential data loss. Try using Chris Mason's torture-test workload with async-checksums without this patch; you will get data corruption if you try dropping power while his torture-test is running. I know you really don't like the barrier, but I'm afraid it's not safe to run without it, even with journal checksums. - Ted