Fast forward to 2010, as well as the new kid in town has displaced Xen since the virtualization of choice for Red Hat and resides in the mainline Linux kernel. Which one to pick? Read on for our appearance at the condition of Xen vs. KVM.

And KVM does not yet have the technical benefit anyway. Since Xen has been around a bit longer, additionally, it has had more time to grow than KVM. You'll get some attributes in Xen that have not yet emerged in KVM, although the KVM job has a lengthy TODO list that they are concentrating on. The list is not an immediate fit for parity with Xen, only a great idea about what the KVM folks intend to work on. In this article here is guide for KVM or Xen Choosing a Virtualization Platform.

KVM and Xen

KVM does have a small advantage in the Linux camp of being the anointed mainline hypervisor. If you're obtaining a current Linux kernel, you have already got KVM built-in. Red Hat Enterprise Linux 5.4 included KVM support as well as the firm are dropping Xen support for KVM in RHEL 6.

That is, in part, an endorsement of just how far KVM has come technically. Does Red Hat have the advantage of using much of the talent behind KVM, but there is also the advantage of introducing friction to firms which have cloned Red Hat Enterprise Linux and invested heavily in Xen. By dropping Xen in the roadmap, they are forcing other companies to drop Xen or pick up maintenance of Xen and diverging from RHEL. This implies additional engineering costs, requiring more effort for ISV certifications, etc..

Xen can do complete virtualization on programs that support virtualization extensions but can also work as a supervisor on machines which don't have the virtualization extensions.

The option of KVM vs. Xen is as likely to be ordered by your vendors as anything else. If you are going with RHEL over the long haul, then bank on KVM. If you are running on Amazon's EC2, you are already using Xen, etc. The significant Linux vendors appear to be standardizing on KVM, but there is loads of commercial service out there for Xen. Citrix probably is not going away anytime soon.

It is tempting in the IT industry to consider technology as a zero-sum game where one alternative wins and another loses. The simple truth is that Xen and KVM will co-exist for many years to come. The market is large enough to support many solutions, and there is enough backing behind the two technologies to make certain they do well for many years to come.

KVM is a hypervisor that's in the mainline Linux kernel. Your host OS needs to be Linux, of course, but it supports Linux, Windows, Solaris, and BSD guests. It follows that KVM is not an option on older CPUs made prior to the virtualization extensions were developed, and it rules out newer CPUs (like Intel's Atom CPUs) that do not include virtualization extensions.

For the most part, that is not an issue for data centres that generally replace hardware every few years anyway -- but it means that KVM is not a choice on some of the market systems such as the SM10000 that are attempting to utilize Atom CPUs from the data center.

There Can Be Only One? KVM and Xen

If you would like to conduct a Xen host, you want to get a supported kernel. Linux does not come with Xen host service from the box, though Linux has been shipping with assistance to run natively as a guest because the 2.6.23 kernel. Instead, you will need to choose a Linux distro that ships with Xen service or build a custom kernel. Or go with one of those business solutions based on Xen, such as Citrix XenServer. The thing is that those solutions aren't entirely open source.

KVM is not entirely on par with Xen, even though it's catching up fast. It's matured enough that lots of organizations feel comfortable deploying it in production. So, does that imply Xen is on the way out?

Xen is running on rather a great deal of servers, from low-cost Virtual Private Server (VPS) providers like Linode to big boys such as Amazon with EC2. A TechTarget article demonstrates how suppliers that have invested heavily in Xen are unlikely to switch lightly. Even if KVM surpasses Xen technically, they are unlikely to tear and replace the present solutions so as to benefit from a slight technical advantage.

Matters in virtualization land move fairly quickly. If you do not have enough time to keep up with the advancements in KVM or Xen development, it is somewhat confusing to choose which (if either) you need to pick.