From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx1.redhat.com (mx1.redhat.com [172.16.48.31]) by int-mx1.corp.redhat.com (8.11.6/8.11.6) with ESMTP id iATFGxr09079 for ; Mon, 29 Nov 2004 10:16:59 -0500 Received: from mail.software.plasmon.com (mail@mail.software.plasmon.co.uk [194.130.136.212]) by mx1.redhat.com (8.12.11/8.12.11) with ESMTP id iATFGvai027495 for ; Mon, 29 Nov 2004 10:16:58 -0500 Received: from leo.devel.pcs ([10.4.2.17] ident=mail) by mail.software.plasmon.com with esmtp (Exim 3.35 #1 (Debian)) id 1CYnGk-0006ZY-00 for ; Mon, 29 Nov 2004 15:16:50 +0000 Received: from steve by leo.devel.pcs with local (Exim 3.36 #1 (Debian)) id 1CYnGj-0006gz-00 for ; Mon, 29 Nov 2004 15:16:49 +0000 Date: Mon, 29 Nov 2004 15:16:49 +0000 From: Steve McIntyre Subject: Re: [linux-lvm] Snapshots (overheads and 2.6 kernel status) Message-ID: <20041129151630.GD1506@software.plasmon.com> References: <37E80E80B681A24B8F768D607373CA80010A5454@largo.campus.ncl.ac.uk> Mime-Version: 1.0 Content-Disposition: inline In-Reply-To: <37E80E80B681A24B8F768D607373CA80010A5454@largo.campus.ncl.ac.uk> 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: LVM general discussion and development On Mon, Nov 29, 2004 at 03:08:50PM -0000, C R Ritson wrote: >Does anybody know how much overhead is involved in keeping a snapshot of >an active volume (for 24 hours)? I am currently running LVM1 (waiting >for snapshots in LVM2/device mapper) and am making a snapshot of my user >volumes overnight. These are left available for 24 hours in the hope >that users who damage a file will be able to get "yesterday's copy" from >the snapshot without us needing to restore from tape. There is obviously >some overhead involved, but does anyone know how much? It can be quite significant, depending on your workload. I'm using snapshots in a similar way, and I saw performance drop by a factor of 2 (or more) on our main NFS server. It's very useful to have the snapshot, so we live with it. -- Steve McIntyre, Plasmon smcintyre@software.plasmon.com "C++ ate my sanity" -- Jon Rabone