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 mA9Fleni010058 for ; Sun, 9 Nov 2008 10:47:40 -0500 Received: from ciao.gmane.org (main.gmane.org [80.91.229.2]) by mx3.redhat.com (8.13.8/8.13.8) with ESMTP id mA9FktOG026048 for ; Sun, 9 Nov 2008 10:47:05 -0500 Received: from list by ciao.gmane.org with local (Exim 4.43) id 1KzCV0-00010J-VP for linux-lvm@redhat.com; Sun, 09 Nov 2008 15:46:50 +0000 Received: from p57a0dd5f.dip.t-dialin.net ([87.160.221.95]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Sun, 09 Nov 2008 15:46:50 +0000 Received: from gator_ml by p57a0dd5f.dip.t-dialin.net with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Sun, 09 Nov 2008 15:46:50 +0000 From: Peter Daum Date: Sun, 09 Nov 2008 16:46:36 +0100 Message-ID: Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: news Subject: [linux-lvm] write performance with active snapshot 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"; format="flowed" To: linux-lvm@redhat.com Hi, for an application I am just working on it looks like lvm snapshots would be just what I need as far as functionality is concerned. Unfortunately, I am experiencing such a massive degradation in performance, that the result is almost useless. I'm working on a fairly fast machine (Quadcore, 8GB RAM) with a big hardware RAID array and lvm2 (Debian Lenny; Linux 2.6.26-1-amd64; LVM version:2.02.39 (2008-06-27) Library version: 1.02.27 (2008-06-25) Driver version: 4.13.0) Sequentially writing to a file (ext3) on a logical volume, I get a sustained performance of ~ 250 MB/sec. When I create a snapshot volume, the write throughput drops to 7-8 MB/secs (on the original volume; writing to the snapshot I see a significant degradation, but not nearly, as bad; read performance is o.k.).Is this "normal" or is there anything I can do to about it? I looked in this list and searched the WWW but couldn't find any concrete information on the performance impact of snapshots (except http://www.nikhef.nl/~dennisvd/lvmcrap.html). It seems like write performance should probably be less then 1/3 of the original throughput, because every write to the source volume causes 3 I/O operations plus some overhead for meta data. More difficult to estimate would be the time lost by additional head movements. Still, a throughput degradation by a factor of 30 seems pretty extreme. Any ideas? Regards, Peter Daum