From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas Mueller Subject: Re: Poor Write I/O Performance on KVM-79 Date: Mon, 5 Jan 2009 14:27:59 +0000 (UTC) Message-ID: References: <66c93b820901032203yc735b1g48d5bf19deffbfc@mail.gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit To: kvm@vger.kernel.org Return-path: Received: from main.gmane.org ([80.91.229.2]:47919 "EHLO ciao.gmane.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754017AbZAEO2M (ORCPT ); Mon, 5 Jan 2009 09:28:12 -0500 Received: from list by ciao.gmane.org with local (Exim 4.43) id 1LJqR7-0007S9-85 for kvm@vger.kernel.org; Mon, 05 Jan 2009 14:28:09 +0000 Received: from 77-58-232-244.dclient.hispeed.ch ([77.58.232.244]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Mon, 05 Jan 2009 14:28:09 +0000 Received: from thomas by 77-58-232-244.dclient.hispeed.ch with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Mon, 05 Jan 2009 14:28:09 +0000 Sender: kvm-owner@vger.kernel.org List-ID: On Sat, 03 Jan 2009 22:03:20 -0800, Alexander Atticus wrote: > Hello! > > I have been experimenting with KVM and have been experiencing poor write > I/O performance. I'm not sure whether I'm doing something wrong or if > this is just the current state of things. > > While writing to the local array on the node running the guests I get > about 200MB/s from dd (bs=1M count=1000) or about 90MB/s write > performance from iozone (sequencial) when I write to a 2G file with a > 16M record length. The node is an 8 disk system using 3ware in a RAID50 > configuration. It has 8GB of RAM. > > The guests get much slower disk access. The guests are using file based > backends (tried both qcow2 and raw) with virtio support. With no other > activity on the machine, I get about 6 to 7MB/s write performance from > iozone with the same test. Guests are running Debian lenny/sid with > 2.6.26-1-686. > > ... > > KVM command to launch guest: > > # /usr/bin/kvm -S -M pc -m 1024 -smp 1 -name demo4 \ -uuid > 5b474147-f581-9a21-ac7d-cdd0ce881c5c -monitor pty -boot c \ -drive > file=/iso/debian-testing-i386-netinst.iso,if=ide,media=cdrom,index=2 \ > -drive file=/srv/demo/demo4.img,if=virtio,index=0,boot=on -net \ > nic,macaddr=00:16:16:64:e6:de,vlan=0 -net \ > tap,fd=15,script=,vlan=0,ifname=vnet1 -serial pty -parallel none \ -usb > -vnc 0.0.0.0:1 -k en-us > if you use qcow2 image with kvm-79 you have to use cache=writeback parameter to get some speed. see also this post from Anthony Liguori: http://thread.gmane.org/gmane.comp.emulators.kvm.devel/24765/focus=24811 - Thomas