Malinka Rellikwodahs wrote:
On Mon, Mar 2, 2009 at 16:22, Anthony Liguori <anthony@xxxxxxxxxxxxx> wrote:
Malinka Rellikwodahs wrote:
What version of kvm is this? Is it kvm-68? You'll have better luck
with
something newer than that.
kvm-83 is the one with the problem, kvm-68 is working correctly.
kvm-68 and qcow2 both use cache=writeback by default which is less safe than
cache=writethrough which is now the default.
But performance shouldn't be as bad as your seeing.
Running the kvm-84 install on the qcow image as kvm -m 1024 -drive
file=qcow,boot=on,cache=writethrough, I get similar performance to the
raw performance.
So it looks like with cache set to writethrough there's a big
performance hit on this setup, any ideas where to look for that?
cache=writeback is "fake" performance. In theory, it should be better
than native because it's being loose with data consistency. So the real
question is why is performance so bad.
It's probably got something to do with IDE. It could be that kvm-84's
IDE is pre-Avi's AIO implementation such that you're splitting up IDE
requests into something small. They should be submitted in parallel but
maybe that's not working out well with your disk setup.
Regards,
Anthony Liguori
Regards,
Anthony Liguori
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