On the same box I tested the following write test dd if=/dev/zero of=test bs=16k count=16k conv=fdatasync and got the following results
OpenVz 52MB/s
KVM 6MB/s
I setup OpenVZ manually on CentOS (since Cloudmin GPL doesn’t support OpenVZ unforunately), and KVM via Clouldmin (using the default settings, e.g. virtio)
Any idea why there is such a difference in write performance?
Well, all Cloudmin is doing is provision Virtual Machines using the tools available to your distribution. It’s not responsible for good or bad performance (similar to how Virtualmin isn’t responsible for Apache’s performance). Cloudmin simply makes VPS’s available.
There are likely to be performance differences between various virtualization types. The way that OpenVZ and KVM perform their virtualization is quite different, and you may be running into differences in how they each work.
KVM provides much better isolation between the various VM’s, where OpenVZ has less isolation, but runs everything from within a single kernel. That may allow OpenVZ to be more efficient.
Yes, same machine and same distribution (CentOS 5.6) with a reinstall before each test. Regarding Kernel I am not so sure, since OpenVZ requires a custom kernel, right?
Yes, OpenVZ and KVM tests were based on the same kernel version 2.6.18. I actually also tried LVM for KVM instead of file images. But the result was virtually the same.
I wonder what your test results were (in case you tried)?
Thanks for the test. I think in another topic you mentioned that the test on your host was 99MB/s, but KVM gets 108MB/s. Is there an explanation? Doesn’t make sense to me.