Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753024AbYLZSIE (ORCPT ); Fri, 26 Dec 2008 13:08:04 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751098AbYLZSHx (ORCPT ); Fri, 26 Dec 2008 13:07:53 -0500 Received: from BISCAYNE-ONE-STATION.MIT.EDU ([18.7.7.80]:64649 "EHLO biscayne-one-station.mit.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750953AbYLZSHw (ORCPT ); Fri, 26 Dec 2008 13:07:52 -0500 Date: Fri, 26 Dec 2008 13:06:42 -0500 From: Theodore Tso To: Alberto Bertogli Cc: linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, dm-devel@redhat.com Subject: Re: jbd2 inside a device mapper module Message-ID: <20081226180642.GO9871@mit.edu> Mail-Followup-To: Theodore Tso , Alberto Bertogli , linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, dm-devel@redhat.com References: <20081224211038.GT4127@blitiri.com.ar> <20081224234915.GA23723@mit.edu> <20081225143535.GA4127@blitiri.com.ar> <20081225155248.GJ9871@mit.edu> <20081226000005.GB4127@blitiri.com.ar> <20081226033736.GK9871@mit.edu> <20081226161708.GC4127@blitiri.com.ar> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20081226161708.GC4127@blitiri.com.ar> User-Agent: Mutt/1.5.17+20080114 (2008-01-14) X-Spam-Flag: NO X-Spam-Score: 0.00 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1092 Lines: 27 On Fri, Dec 26, 2008 at 02:17:08PM -0200, Alberto Bertogli wrote: > > At this moment I'm trying to keep it simple, so I plan to batch two for > each sector written to the device: one for the metadata and one for the > data. > I think I can pretty much guarantee that your performance will be so horrible that it won't be worth using. > > Yes, this is necessary because in a production system you need to be > > able to identify the external journal by UUID, and the ext2/3/4 > > superblock makes it easy to add a label, UUID, et. al. It also > > significantly lowers the chance that an external journal will get > > misidentified as some other filesystem based on the data stored in the > > journal. > > Yes, it makes sense. I've reserved the first sector for that purpose. Why not just use the ext3/4 external journal format? - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/