[Oneiric-Topic] Revisit Xen support

Serge van Ginderachter serge at vanginderachter.be
Mon Apr 4 11:16:05 UTC 2011

On 4 April 2011 12:31, Soren Hansen <soren at linux2go.dk> wrote:

> 2011/4/2 Serge van Ginderachter <serge at vanginderachter.be>:
> > On 2 April 2011 16:58, Clint Byrum <clint at ubuntu.com> wrote:
> >> Serge, would you mind elaborating on that? I'm looking for facts.
> >
> > I tested several virtualisation technologies last year.
> I'm terribly sorry, but this information is practically useless. There

Yes, I very well realise that. I only gave some general concusions to give
an idea of what we were looking at.
I was only trying to slightly elaborate on the matter as an answer to an
earlier question on the list.

Unfortunately, the reports of those tests are private and not published, and
I'm not allowed to do that (don't ask), so I can't fully disclose them.

> are no version numbers, no information about configuration, about
backing stores, disk image formats, cache settings, and very little
> about hardware, etc. I can't e.g. tell if your factor 8 drop i
> performance on Ubuntu for small writes is due to the virtual disk
> being backed by a qcow2 on ext4, for instance, and as such, I can't
> use the data (and much less the conclusions) for anything.

Yes, lots of things could be optimised, that's for sure. But the main aim of
the tests were primarily about comparing Xen and KVM, and as such, similar
setups (LVM backed disks, Virtio/HVM hardware, using the same startup
scripts on all platforms, ... ) and pretty much most default settings were
used. The VM images were all identical, Debian Lenny with ext3.

So, while different settings might not be fully optimized in those tests -
at the time we were pretty new with this stuff - we did made several tests
which could compare different platforms. And our conclusion to that was that
KVM in general was less performant than Xen.

That is the only point I wanted to make. Obviously, YMMV.

Also note that these conclusions don't stop me from still using Ubuntu+KVM
for lots of setups, but more because of ease of use than performance.

Met vriendelijke groet,
Serge van Ginderachter
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