KVM requires virtualization hardware, and the hard-drive is QUEMU, slow, and
they don't even have plans to para-virtualize it. I tested the virtio
drivers with the current KVM and my virtual machines blew up under pressure.
It is not fully-baked yet.
But let's define the terms: Windows on Xen requires VTD, or
Virtualization-hardware. That is sloooow performance compared with Microsoft
Hyper-V R2, maybe a half. SMP is poor, poor. Hyper-V gives a good two way
and declines exponentially after that, so the most you can do is two-way. I
have over 150 windows 2003 virtual machines in production.
On the other hand, Xen domu's is Linux on Linux, and it flies. That is what
I call para-virtualization, and I have over 100 of those machines. Vmware,
on the other hand, is useless. For example, ESXi does fully-virtualize
everything, even Linux domu's, offering maybe 1/2 of the aggregated
performance you can get with, for instance, Suse as host and Centos a Domu.
Let's be clear, Novell tech support does not "support" Centos or Red Hat as
paravirtualized domu's, but it works so much faster that you would be an
idiot not to do it, and it is 100% stable I have 100% of my company's
business in paravirtualized Domu's under Novell's Suse. There is a powerful
reason to prefer Suse as host instead of Red Hat (I have both licenses). If
you have a problem, a real problem, Novell actually logs into the server and
tries to understand the issue, with a human being. Red Hat is hands-off, I
mean, they are not allowed to log into your server. The support is
absolutely deficient for a company that cannot go down.
So my 5 cents of advice is: Novell as a Host, Centos as Linux Domu or
Ubuntu, if you like it (it works), and keep a separate machine for all your
windows users. Do not mix them.
[mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Freddie Cash
Sent: Thursday, February 26, 2009 6:52 PM
Subject: Re: [Xen-users] I want to know if.....
On February 26, 2009 3:32 pm Venefax wrote:
> It is not true at all. KVM and Xen are fundamentally different and
> address different problems. Xen allows for fast para-virtualization of
> Linux Domus, while KVM only fully-virtualizes. Nobody in his right mind
> would use KVM for a linux DOMu, because it would lose 75% of its
> performance, compared to para-virtualization. So KVM is for windows on
> Xen, but it will never replace Xen in the datacenter.
I think you are confusing HVM (hardware-assisted VMs), which both KVM and
Xen support, with KVM (kernel-based VM), another virtualisation system.
KVM has paravirtualised network, block/storage, and console drivers for
Linux and Windows. Same as Xen. There's no "75% loss of performance".
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