Re: Set nodatacow per file?

[dima <dolenin@parallels.com>]

On 02/13/2012 04:17 PM, Ralf-Peter Rohbeck wrote:
> Hello,
> is it possible to set nodatacow on a per-file basis? I couldn't find
> anything.
> If not, wouldn't that be a great feature to get around the performance
> issues with VM and database storage? Of course cloning should still
> cause COW.

Hello,
Going back to the original question from Ralf I wanted to share my 
experience.

Yesterday I set up KVM+qemu and set -z -C with David's 'fileflags' 
utility for the VM image file.
I was very pleased with results - Redhat 6 Minimal installation was 
installed in 10 minutes whereas it was taking 'forever' the last time I 
tried it some 4 months ago. Writes during installation were very 
moderate. Performance of VM is excellent. Installing some big packages 
with yum inside VM goes very quickly with the speed indistinguishable 
from that of bare metal installs.

I am not quite sure should this improvement be attributed to the nocow 
and nocompress flags or to the overall improvement of btrfs (I am on 
3.3-rc4 kernel) but KVM is definitely more than usable on btrfs now.

I am yet to test the install speed and performance without those flags set.

best
~dima