On Mon, 26 Mar 2012, Martin van Wilderen - JDN BV wrote: > Hi Scott, > > kvm --version > QEMU emulator version 0.13.91 (qemu-kvm-0.14.0-rc1), Copyright (c) 2003-2008 > Fabrice Bellard > > virsh --version > 0.8.8 > > uname -r > 2.6.35-22-server > > Need any more info?
Well, unfortunately there is lots more info needed, and I'm not really able to dedicate resources to debugging this at this point. I was curious because I had circumstantial evidence pointing to qemu-kvm 1.0 (in ubuntu 12.04) being slower than 11.10. However, your data above is similar to what I've seen in 12.04. Most definitely, if you want write performance, you will need fully allocated disks. The qcow sparse is good for quick deployment, but not good for write speed. You may also want to try using qed format disk as that is supposed to be a bit better. I had one kvm person suggest looking at barriers of the host's ext4 filesystem, saying: if you have ext4 filesystem underneath with barriers enabled, then you'll find that the guest will submit barriers to the host filesystem which will end up flushing the device cache A quick google showed http://blog.smartlogicsolutions.com/2009/06/04/mount-options-to-improve-ext4-file-system-performance on generally how to get some additional performance out of ext4. I'm interested in hearing what you find out, but unfortunately at the moment, I dont' have a magic bullet for you. > > Met vriendelijke groet, > > Martin van Wilderen > Technical Manager > > On Mar 26, 2012, at 5:12 PM, Scott Moser wrote: > > > Can you provide information about what version of kvm you're using ? > > I suspect this is really unrelated to openstack specifically. > > > > On Mon, 26 Mar 2012, Martin van Wilderen - JDN BV wrote: > > > >> Hi List, > >> > >> I have a question about KVM disk performance. We are using Openstack Nova > >> on three machines. These machines have a SSD drive with a dd write > >> performance of about 130mb/s > >> > >> Within the instance the write performance is down to about 5 mb/s. When > >> using the allocate trick (dd zero to disk before newfs) we get a > >> performance of 20 mb/s. > >> > >> Things a have tried but don't give any extra results are: > >> - Settings the disklayout from qcow2 to raw > >> - Settings the cache type in libvirt.xml (writeback, writethrough, none) > >> - Switching KSM on and off. > >> - Tested with different guests OS, Linux, FreeBSD, Windows. > >> > >> Is there someone who had some extra info i can check? Or are there more > >> people with this issue? > >> > >> Snippet from libvirt.xml > >> <driver type='qcow2'/ cache='writeback'/> > >> <source file='/var/lib/nova/instances/instance-00000113/disk'/> > >> <target dev='vda' bus='virtio'/> > >> > >> Kind regards, > >> > >> Martin > >> _______________________________________________ > >> Mailing list: https://launchpad.net/~openstack > >> Post to : [email protected] > >> Unsubscribe : https://launchpad.net/~openstack > >> More help : https://help.launchpad.net/ListHelp > >> > >> > > _______________________________________________ Mailing list: https://launchpad.net/~openstack Post to : [email protected] Unsubscribe : https://launchpad.net/~openstack More help : https://help.launchpad.net/ListHelp
