Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262366AbTESIGU (ORCPT ); Mon, 19 May 2003 04:06:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262367AbTESIGU (ORCPT ); Mon, 19 May 2003 04:06:20 -0400 Received: from unthought.net ([212.97.129.24]:32917 "EHLO unthought.net") by vger.kernel.org with ESMTP id S262366AbTESIGS (ORCPT ); Mon, 19 May 2003 04:06:18 -0400 Date: Mon, 19 May 2003 10:19:14 +0200 From: Jakob Oestergaard To: Anders Karlsson Cc: Riley Williams , Clemens Schwaighofer , LKML Subject: Re: Two RAID1 mirrors are faster than three Message-ID: <20030519081914.GB14971@unthought.net> Mail-Followup-To: Jakob Oestergaard , Anders Karlsson , Riley Williams , Clemens Schwaighofer , LKML References: <1052995874.3248.20.camel@tor.trudheim.com> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1052995874.3248.20.camel@tor.trudheim.com> User-Agent: Mutt/1.3.28i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1833 Lines: 43 On Thu, May 15, 2003 at 11:51:14AM +0100, Anders Karlsson wrote: ... > No, it should not cause problems as when you add the split-off copy back > into the mirror, it is treated as 'stale' and will get synchronised with > the original. Correct If this was not the case, background resynchronization of standard 2-disk RAID-1 would be a really horrible feature (with half the reads returning stale data from the new disk)... > > I would be very surprised if the Linux software md driver worked any > diffrently than this. Perhaps someone that knows it in-depth can add to > the conversation? Unless there's bugs in the driver, your description is correct :) > > With the facilities of LVM 'snapshots' now being available, this > practice of splitting off one copy from a three-way mirror is perhaps > becoming redundant, but people will likely take the approach of "if it > ain't broken, don't fix it" and leave old backup methods as they are. > So if you work in the sysadm field, you might well come across this > practice. The really good argument for N>2 disk RAID-1 is still the seek-time and multiple-readers performance benefits which you won't be addressing with LVM snapshots. -- ................................................................ : jakob@unthought.net : And I see the elder races, : :.........................: putrid forms of man : : Jakob ?stergaard : See him rise and claim the earth, : : OZ9ABN : his downfall is at hand. : :.........................:............{Konkhra}...............: - 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/