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Re: KVM disk performance


Hi Scott,

kvm --version
QEMU emulator version 0.13.91 (qemu-kvm-0.14.0-rc1), Copyright (c) 2003-2008 Fabrice Bellard

virsh --version

uname -r

Need any more info?

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
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