On Mon, 15 Aug 2011 16:05:17 -0600, Orion Poplawski wrote:
I have a server that I recently migrated from CentOS 5.6 to SL6.1.
The host install serves as a basic disk server and runs our nightly
backups with amanda. We also have several virtual machines running
on
it, so of which are mostly idle and others which can be quite busy.
Since making the move I'm seeing the disk and network
response/performance go to hell if I have any non-idle VMs running.
One barometer - I have a raid10 rebuild running at the moment. With
no VMs I can reach 200,000K/sec resync speed. I'm getting 131,000K
with two idle VMs and some other basic activity. If I start a busy
vm, it drops to a few hundred K/sec and all disk access is very slow.
Response to keystrokes in a network shell can be very slow as well.
As anyone else experienced problems like this? I'm not seeing any
error messages on the host or VMs.
Hi,
The default settings are bad.
Please tell us more about your settings.
Otherwise, I recommend the following points:
- controller: virtio
- kvm option: cache=none
- qcow2 disk format with metadata preallocation
- create your disk image with: qemu-img create -f qcow2 -o
size=40000000000,preallocation=metadata vdisk.img
Here's a good link to the topic:
http://www.ilsistemista.net/index.php/virtualization/11-kvm-io-slowness-on-rhel-6.html
Best regards,
Morten
