[Oneiric-Topic] Revisit Xen support

Serge van Ginderachter serge at vanginderachter.be
Sat Apr 2 16:23:23 UTC 2011

On 2 April 2011 16:58, Clint Byrum <clint at ubuntu.com> wrote:

> > > Other than people already having familiarity with Xen, what is a
> > > compelling reason to support it in favor of, or in addition to, KVM?

> > Performance.

> Serge, would you mind elaborating on that? I'm looking for facts.

I tested several virtualisation technologies last year.

I told my conclusions earlier on another list, but I'll copy paste them here
for easier follow-up:


About a small year ago, I have been conducting some various tests on
comparing different virtualisation technologies on different

* tested VMWare ESXi, Xen on Debian and CentOS and KVM on Ubuntu and CentOS
* these tests have nothing to do with Ganeti, nor was there a test with
* on Xen and KVM I tested using HVM/Virtio - not so on VMWare
* made different tests, stressing CPU, disk, memory and network on 1
till 10 concurrent vm's.
* client vm machines were all Debian Lenny

Some general conclusions were:

* VMWare ESXi was the clear winner,
* Xen on Debian Lenny was a close second, and the winner amongst Open
Source solutions.
* Xen performance is way better than KVM, especially when looking at disk
* Xen performs in a more stable and predictable way, whilst KVM seemed
to perform more at random (which confirms Iustin's observations, )
* CentOS (5.4) performed remarkably well for being older sofwtare
versions (KVM, Xen, Linux kernel)
* performance on Ubuntu was really bad. The then recent Ubuntu Lucid
was far worse than CentOS 5.5 (both KVM)

* Disk speed on bare metal was 80MB/s
* on vm, those dropped to 40-20MB/s depending on the platform end
thenumber of concurrent access (= number of tested vm's)

Also, testing latency (lots of small writes): time dd if=/dev/zero
of=/dev/vda5 bs=512 count=100000 oflag=direct

* 4.6 MB/s on bare metal
* 728 KB/s on vm Ubuntu + KVM
* on vm Debian Lenny + Xen:don't have the number anymore but noted a
performance drop of only 20%

It really struck me how Ubuntu's performance was really bad, even when
comparing the then recent Lucid to a Red Hat backported kernel (still

Of course, lots of things have evolved since then, but when looking at the
major distro's, to update conclusions, one should look at Debian Squeeze and
Red Hat 6.
At least for Ubuntu, no things have changed if you only consider Ubuntu LTS
as a contender (which is how I look at it at least).

Met vriendelijke groet,
Serge van Ginderachter
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