----- Message from "Brian J. Murrell" <brian@xxxxxxxxxxxxxxx> ---------
Date: Thu, 15 Dec 2011 14:43:23 -0500
From: "Brian J. Murrell" <brian@xxxxxxxxxxxxxxx>
Subject: Re: 5x slower guest disk performance with virtio disk
To: kvm@xxxxxxxxxxxxxxx
Cc: Sasha Levin <levinsasha928@xxxxxxxxx>
On 11-12-15 12:27 PM, Daniel P. Berrange wrote:
On Thu, Dec 15, 2011 at 07:16:22PM +0200, Sasha Levin wrote:
On Thu, 2011-12-15 at 11:55 -0500, Brian J. Murrell wrote:
So, about 2/3 of host speed now -- which is much better. Is 2/3 about
normal or should I be looking for more?
aio=native
Thats the qemu setting, I'm not sure where libvirt hides that.
<disk ...>
<driver io='threads|native'/>
...
</disk>
When I try to "virsh edit" and add that "<driver io=.../>" it seems to
get stripped out of the config (as observed with "virsh dumpxml").
Doing some googling I discovered an alternate syntax (in message
https://www.redhat.com/archives/libvirt-users/2011-June/msg00004.html):
<driver name='qemu' type='raw' cache='none' io='native'/>
But the "io='native'" seems to get stripped out of that too.
FWIW, I have:
qemu-kvm-0.12.1.2-2.113.el6.x86_64
libvirt-client-0.8.1-27.el6.x86_64
installed here on CentOS 6.0. Maybe this aio= is not supported in the
above package(s)?
You need to update CentOS, your version of libvirt does not support
io=native I don't believe. You are running into similar issues that I
have posted about (mostly unsuccessfully in terms of getting much
support LOL) here -
https://www.centos.org/modules/newbb/viewtopic.php?topic_id=33708&forum=55
From that thread:
With libvirt 0.8.7-6, qemu-kvm 0.12.1.2-2.144, and kernel 2.6.32-115,
you can use the "io=native" parameter in the KVM xml files. Bugzilla
591703 has the details, but basically my img file references in the VM
xml now reads like this:
<disk type='file' device='disk'>
<driver name='qemu' type='raw' cache='none' io='native'/>
<source file='/vm/pool/server06.img'/>
<target dev='vda' bus='virtio'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x04'
function='0x0'/>
</disk>
You may also want to search this list for my thread from November with
the title "Improving RAID5 write performance in a KVM VM"
Cheers
Simon.
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