From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx3.redhat.com (mx3.redhat.com [172.16.48.32]) by int-mx1.corp.redhat.com (8.13.1/8.13.1) with ESMTP id n1N7BpmM015461 for ; Mon, 23 Feb 2009 02:11:51 -0500 Received: from e5.ny.us.ibm.com (e5.ny.us.ibm.com [32.97.182.145]) by mx3.redhat.com (8.13.8/8.13.8) with ESMTP id n1N7BY2Y017665 for ; Mon, 23 Feb 2009 02:11:34 -0500 Received: from d01relay02.pok.ibm.com (d01relay02.pok.ibm.com [9.56.227.234]) by e5.ny.us.ibm.com (8.13.1/8.13.1) with ESMTP id n1N78jph014805 for ; Mon, 23 Feb 2009 02:08:45 -0500 Received: from d01av02.pok.ibm.com (d01av02.pok.ibm.com [9.56.224.216]) by d01relay02.pok.ibm.com (8.13.8/8.13.8/NCO v9.1) with ESMTP id n1N7BXj3192064 for ; Mon, 23 Feb 2009 02:11:33 -0500 Received: from d01av02.pok.ibm.com (loopback [127.0.0.1]) by d01av02.pok.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id n1N7ALKt012647 for ; Mon, 23 Feb 2009 02:10:21 -0500 Received: from malahal.localdomain (malahal.beaverton.ibm.com [9.47.17.130]) by d01av02.pok.ibm.com (8.12.11.20060308/8.12.11) with ESMTP id n1N7AKQF012634 for ; Mon, 23 Feb 2009 02:10:20 -0500 Date: Sun, 22 Feb 2009 23:11:32 -0800 From: malahal@us.ibm.com Subject: Re: [linux-lvm] re --corelog: does synchronization re-copy all data? Message-ID: <20090223071132.GA9670@us.ibm.com> References: <49A0A252.30803@smart.net> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <49A0A252.30803@smart.net> Reply-To: LVM general discussion and development List-Id: LVM general discussion and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , List-Id: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-lvm@redhat.com Daniel B. [dsb@smart.net] wrote: > In the LVM Administrator's Guide, at least the one at > http://www.centos.org/docs/5/html/Cluster_Logical_Volume_Manager/LV_create.html , > it says:" > > LVM maintains a small log which it uses to keep track of which regions > are in sync with the mirror or mirrors. By default, this log is kept > on disk, which keeps it persistent across reboots. You can specify > instead that this log be kept in memory with the --corelog argument; > this eliminates the need for an extra log device, but it requires that > the entire mirror be resynchronized at every reboot. > > Does that last sentence mean that _all_ the data is recopied, or just > that all _regions_ are checked and not all the data necessarily has > to be copied (perhaps only change regions have to be copied, but > unchanged regions don't)? Everything has to be re-copied because it doesn't know what is changed as the "log" is kept in memory which is lost after a reboot. > More generally, can LVM perform RAID1-style mirroring with only > two disks (without having to re-copy everything each boot) > (and, of course, being recoverable in case either disk fails)? You should be able to force LVM to create a log device on one of your two devices (--alloc anywhere) Thanks, Malahal.