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Re: KVM disk performance


Hi Martin

   1. Does /var/lib/nova/instances reside on your SSD? (just double
   checking it's not instead pointing to a normal stoage device).
   2. Do you see the expected performance on the host operating system?
   3. Could you please provide the complete libvirt .xml file?
   4. Could you please provide the operating system and version of the



On Mon, Mar 26, 2012 at 1:59 PM, Martin van Wilderen - JDN BV <martin@xxxxxx
> 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
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