Why do many consider KVM a better approach than Xen?

Well, here's what one of the KVM developers said in a blog post entitled, The truth about KVM and Xen:

I'm think we can finally admit that we, the Linux community, made a very big mistake with Xen. Xen should have never been included in a Linux distribution. There, I've said it. We've all been thinking it, have whispered it in closed rooms, and have done our bests to avoid it.

I say this, not because Xen isn't useful technology and certainly not because people shouldn't use it. Xen is a very useful project and can really make a huge impact in an enterprise environment. Quite simply, Xen is not, and will never be, a part of Linux. Therefore, including it in a Linux distribution has only led to massive user confusion about the relationship between Linux and Xen.

Xen is a hypervisor that is based on the Nemesis microkernel. Linux distributions ship Xen today and by default install a Linux guest (known as domain-0) and do their best to hide the fact that Xen is not a part of Linux. They've done a good job, most users won't even notice that they are running an entirely different Operating System. The whole situation is somewhat absurd though.

Another reason given is that Xen seems to be doing a lot of code duplication by providing Xen versions of drivers that can already be found in the mainline Linux kernel. In contrast, KVM is a module for Linux that has a codebase that is a fraction of the size of Xen's. KVM adds hypervisor features to Linux using the device drivers that the Linux kernel already has.

At work I'm running Fedora 9 on a Dell Optiplex 755 with Intel Core 2 Duo processor and I've been running KVM using virt-manager. I have used KVM primarily to try out LiveCDs of new Linux distribution releases as well as to run a Microsoft Windows XP desktop that used to be a physical machine. It seems to work rather well and I've been very impressed.

Qumranet - KVM and what else?

While Qumranet's primary claim to fame has been as the sponsor for the bulk of KVM development work their primary business has been selling a closed source (proprietary) Desktop Virtualization environment named Solid ICE. What is it? See this demo video for quick and dirty visual presentation. Sorry, it requires the ability to play Windows Media Video (WMV) files.

SPICE is a patented communications protocol that Qumranet created to provide local desktop performance from remote virtual machines. They claim SPICE is similar to Microsoft's Remote Desktop Protocol (RDP) but with process balancing features that give it a significant performance/speed boost that allows it to do such things as drive upto a 4-head display with full screen HD video and bi-directional audio. If you look at the video, it is quite impressive.

[linuxkernelnewbies] Qumranet Joins Red Hat - Lots of questions | MontanaLinux.org

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