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 (8.13.1/8.13.1) with ESMTP id n0VEpv8r020026 for ; Sat, 31 Jan 2009 09:51:57 -0500 Received: from mail.cs.tu-berlin.de (mail.cs.tu-berlin.de [130.149.17.13]) by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id n0VEpZXH002845 for ; Sat, 31 Jan 2009 09:51:36 -0500 Received: from localhost (localhost [127.0.0.1]) by localhost-12225.cs.tu-berlin.de (Postfix) with ESMTP id 92AF329233 for ; Sat, 31 Jan 2009 15:51:35 +0100 (MET) Received: from mailhost.cs.tu-berlin.de ([127.0.0.1]) by localhost (mail.cs.tu-berlin.de [127.0.0.1]) (amavisd-new, port 12224) with ESMTP id okgOylFzTd2N 25405-05 for ; Sat, 31 Jan 2009 15:51:31 +0100 (MET) 16168 Received: from [127.0.0.1] (fiesta.cs.tu-berlin.de [130.149.17.4]) by mailhost.cs.tu-berlin.de (Postfix) with ESMTP for ; Sat, 31 Jan 2009 15:51:31 +0100 (MET) Message-ID: <4984656F.8060206@yahoo.de> Date: Sat, 31 Jan 2009 15:51:27 +0100 From: Peter Daum MIME-Version: 1.0 References: <1c748a490811100711m7b09f422nb1f4eeced5d2e2bb@mail.gmail.com> <8CB47E27BD0C852-AC4-686@WEBMAIL-DG06.sim.aol.com> In-Reply-To: <8CB47E27BD0C852-AC4-686@WEBMAIL-DG06.sim.aol.com> Content-Transfer-Encoding: 7bit Subject: [linux-lvm] Re: 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: LVM general discussion and development Hi Thomas, thomas62186218@aol.com wrote: > I am following your thread on this topic...have any solutions emerged? I > as well have seen miserably performance when snapshots are active. I am sorry, at least I still don't know any solution (except avoiding snapshots wherever performance matters )-: Regards, Peter > -----Original Message----- > From: Peter Daum > To: linux-lvm@redhat.com > Sent: Tue, 11 Nov 2008 8:04 am > Subject: [linux-lvm] Re: write performance with active snapshot > > > > > > > > > > Hi, > > > Larry Dickson wrote: > >> My guess is that you are getting the typical seek overhead. Have you >> tried making a volume group out of two separate RAID arrays (driving >> different spindles), and using lvdisplay --maps to make sure the > parent >> volume is on one array, the snapshot(s) on the other? > > > That was my suspicion, too (although I could not imagine such an extreme > > impact). Just for testing I added a single disk to the same volume group > > and put the snapshot onto that disk - amazingly it made hardly any > > difference (Actually, I'm almost glad about that, because the combination > > of a 12-disk-array with a single disk would be under almost all other > > aspects foolish). > > > One thing that does improve the performance a little (actually by 100%, > > which in this case meens still pretty lousy 16 MB/sec) is to increase > > the chunk size to 512kb. (I don't know yet, how this might > affect > > performance when dealing with many small files) ... > > > Regards, > > Peter > > > >> On 11/9/08, *Peter Daum* > >> wrote: > >> >> 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 a > nything 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 > > > _______________________________________________ > > linux-lvm mailing list > > linux-lvm@redhat.com > > https://www.redhat.com/mailman/listinfo/linux-lvm > > read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/ > > > > > > Hi > > _______________________________________________ > linux-lvm mailing list > linux-lvm@redhat.com > https://www.redhat.com/mailman/listinfo/linux-lvm > read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/ >