KVM vs XEN vs VMware

Henning Sprang henning_sprang at gmx.de
Thu May 3 17:14:59 UTC 2007

On 5/3/07, Tomoki Taniguchi <tomoki.taniguchi at gmail.com> wrote:
> I am curious about which of the the following virtualization options
> people recommend under Feisty?
> 1) KVM
> 2) XEN
> 3) VMware
> Please take into account I will be running this on a laptop with 1.5GB of RAM.
> Primary use will be to run WinXP
> I may want to use it to test other OSs (linux, FreeBSD, NetBSD)

Not an easy question that can be anserwered with some words. There are
some things to think about:

What usage scenario do you have - do you intend some 2high performance
scenario? What devices do you need to use inside the VM?

With the opensource Version of Xen, IO in windows VM's will be quite
slow - as the drivers are emulated via qemu libs. This goes for KVM as
well, I think (but not sure), because the much-praised Hardware
Virtualization in the processors (which you need to run windows in Xen
as well as for run KVM at all)

With Xen HVM, I never got running FreeBSD and NetBSD seemlessly. These
run easiest on VMWare, or qemu - then again, with much more
performance loss.

> Is it possible to access and use peripherals which the host OS
> does not support?

Hmm, it depends. Paravirtualized xen can forward PCI ports, but it
wasn't there in HVM mode (which you need for Windows). Maybe it's in
the newest 3.0.5 release, which I didn't test yet.

In general, for KVM and Xen, as both use parts of qemu for this, you
have the same devices that are possible to use in qemu - and these
functions can be limited in the area of Hardware-support, because
these devices are emulated.

Put together, I think what you want to do can become a bit hard to do
with Xen and KVM - but it _can_ work. With VMWare, it might be a bit
or even significantly slowe, but _might_ work better - I don#t know
much about VMWare, just used Xen a lot and KVM a bit.

For real power usage, if I had to use windows, I'd still always go
native, not virtualized. Or try XenEnterprise (they have a 100$
version for windows desktop use).

After writing all this, I realize, this has not much to do with
ubuntu/feist - it's mainly a question of evaluating these technologies
according to the intednded use, which is a lot of testing and work -
they should all work quite well on feisty.


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