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Re: KVM disk performance


Hi David,

1. Yes. That's the only disk in the system.

2. Yes:
nova1:/var/lib/nova/instances$ dd if=/dev/zero of=test bs=1M count=256
256+0 records in
256+0 records out
268435456 bytes (268 MB) copied, 2.04146 s, 131 MB/s

4. I have tried with:
- Linux Ubuntu 10.10
- FreeBSD 8.2 with virtio driver
- Windows 2008 R2 Server with virtio driver

3. my libvirt.xml 
<domain type='kvm'>
            <boot dev="hd" />
        <disk type='file'>
            <driver type='raw'/>
            <source file='/var/lib/nova/instances/instance-00000121/disk'/>
            <target dev='vda' bus='virtio'/>
            <disk type='file'>
                <driver type='raw'/>
                <source file='/var/lib/nova/instances/instance-00000121/disk.local'/>
                <target dev='vdb' bus='virtio'/>

        <interface type='bridge'>
            <source bridge='br100'/>
            <mac address='02:16:3e:33:42:e3'/>
            <filterref filter="nova-instance-instance-00000121-02163e3342e3">
                <parameter name="IP" value="" />
                <parameter name="DHCPSERVER" value="" />

        <!-- The order is significant here.  File must be defined first -->
        <serial type="file">
            <source path='/var/lib/nova/instances/instance-00000121/console.log'/>
            <target port='1'/>

        <console type='pty' tty='/dev/pts/2'>
            <source path='/dev/pts/2'/>
            <target port='0'/>

        <serial type='pty'>
            <source path='/dev/pts/2'/>
            <target port='0'/>

        <graphics type='vnc' port='-1' autoport='yes' keymap='en-us' listen=''/>

Met vriendelijke groet,

Martin van Wilderen
Technical Manager

On Mar 26, 2012, at 4:45 PM, David Busby wrote:

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