Re: KVM on top of BTRFS

[dima <dolenin@parallels.com>]

On 06/12/2012 08:53 AM, Alex wrote:
> Matthew Hawn <steamraven <at> yahoo.com> writes:
>> What are the recommendations for running KVM images on BTRFS systems using
> kernel 3.4?  I saw older
>> posts on the web complaining about poor performance, but I know a lot of work
> has gone into btrfs since then.
>>   There also seemed to be the nocow option, but I didn't find anything that
> said it actualy helped.

I don't think it is about the kernel version, but rather about choosing 
the right option for KVM.
I am running KVM via libvirt on btrfs with lzo compression, autodefrag, 
inode and space cache for quite some time. Yes, I did set nocow for the 
directory with images. I have no proof that it actually helps with disk 
images, but being set for the build directory my build time is down 5 
minutes.
I used raw virtio images with no caching. I guess this is the key if we 
talk about disk I/O. The performance looks fine, though I only use it 
for testing.
The last time I tried to install WinXP on KVM it was a disaster. But I 
guess I did not choose the right options, nor did I install virtio 
drivers inside the guest.
VirtualBox still outperforms KVM on btrfs in my view.

best