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Re: [Xen-users] Xen and KVM.

To: "Emre Erenoglu" <erenoglu@xxxxxxxxx>
Subject: Re: [Xen-users] Xen and KVM.
From: "Grant McWilliams" <grantmasterflash@xxxxxxxxx>
Date: Tue, 18 Nov 2008 14:44:40 -0800
Cc: Mauro <mrsanna1@xxxxxxxxx>, xen-users@xxxxxxxxxxxxxxxxxxx, Johannes Schlatow <johannes.schlatow@xxxxxxxxxxxxxx>
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On Tue, Nov 18, 2008 at 12:04 PM, Emre Erenoglu <erenoglu@xxxxxxxxx> wrote:
Hi again,

On Tue, Nov 18, 2008 at 8:53 PM, Johannes Schlatow <johannes.schlatow@xxxxxxxxxxxxxx> wrote:
- afaik no PCI passthrough
- still in development and not as stable as Xen

Well I don't see stability problem on my test systems. For PCI passthough, check out this announcement, it's coming:

My Win2000 Server is far more faster on Xen, maybe this was an issue
with the standard interfaces between dom0 and guest. If you can use
virtio devices (I think the frontend drivers are included since kernel
version 2.6.23 or 2.6.25) there will be no bottle neck anymore.

I find KVM faster. Especially on linux-on-linux virtualizations, KVM with virtio is very fast. Near native in fact.

For Windows guest installations, the virtio network driver is also very fast (above gigabit speeds on a Core2Duo). The emulated disk benchmarks (simple benchmarks) were about 60 meg/sec on a raid0 array of two sata disks.  I guess it will also be very fast if it can be run over a AoE or iScsi host.
With some kernel hacks I newly got Xen running on my hardware (nvidia
630a chipset). So this will be my personal solution for some month.

very difficult, time consuming, hair trimming. I gave up personally after Ubuntu Hardy (2.6.22 dom0 kernel) and switched to KVM on desktop.


KVM is NOT in any way ready for a production environment. Just follow the KVM dev list to see what I'm talking about. The Xen dev list is full of small patches and the KVM dev list is chock full or people ripping out the transmission and crankshaft every week. I give it about a year before I'l start moving it into production. With kvm-78 and kvm-79 there was a huge regression in qcow2 disk images to the tune of 1/10 the performance. Yes, that's about 6MB/sec on a 60MB/sec drive. With kvm-77 you'll get 60MB/sec on that same disk image. These things happen all the time. And if you want to run KVM on an enterprise Linux (Redhat perhaps) you're going to get a really old version. Even if you upgrade it you'll be about 10 version back. You can upgrade Xen to 3.3 fairly easy on RHEL5. Upgrading the kernel to something other than the stock one though is a different story.

Linux on Linux should never be faster on KVM but with virtio drivers for disk and net it should be able to equal Xen in those two areas. Xen currently has some IO issues on inbound network traffic that limits it but outbound runs as fast as anything.

KVM running fulling virtualized should be faster than Xen though if you need to do that for running Windows etc...

Xen however is the most secure VM solution around and with 3.3 and stub domains it got more secure. I follow the KVM dev cycle and use it for test cases but never in a production environment. For Desktop I use VirtualBox and for all servers I use Xen 3.3.

Having said all of this I still track KVM development because in time it will be come THE Virtualization for Linux. However, it's only a Linux solution as it will only run on Linux. Our thinking has a tendency to get a little OS centric sometimes.

Grant McWilliams

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