Why Use Xen?

At the Linux Foundation Collaboration Summit in April, the Xen Project announced that it was now a Collaborative Project of the Linux Foundation.  But as people attended some of the Xen-related conference sessions, one question always seemed to be asked: “Why should I use Xen?”

There is an answer – but it varies depending on the audience.

Xen logo and pandaFor the business person, the answer is that Xen is a safe, stable, well-tested choice for virtualization which is used by industry giants (Amazon, Rackspace, Verizon, etc.).  It has a robust consortium of companies behind its development and it has the price, performance, and security to go toe-to-toe with the best offerings in the industry.  Plus, it has a proven 10-year track record which includes powering some of the largest clouds in the world.

For tech-savvy users of F/OSS, however, there are additional considerations.  A few of these include:

·         Type 1 Hypervisor: The fact that the Xen Project employs a Type 1 Hypervisor – a hypervisor that runs on bare metal rather than within an existing operating system kernel. This means its architecture has special attributes when it comes to scale, security, and performance.

·         Disaggregation: The ability to segment individual device drivers into small, nimble Driver Domains means that device-related performance bottlenecks can be reduced or eliminated.  It also means that device drivers that might be subject to attack by crackers can be segmented from the rest of the environment and even refreshed regularly to remove any compromise that may be incurred.  Similarly, an unstable device driver can be isolated via disaggregation and easily rebooted if it should fail.

·         Flexible Virtualization Modes: The hypervisor provides different virtualization modes which allow the administrator to adapt to the specifics in the workload and capabilities of the hardware.  In particular, Xen pioneered the now popular concept of a paravirtualization (PV) mode offering an extremely optimized low-overhead experience for many workloads.

·         Multiple Architectures: The software can run on traditional x86 32-bit and 64-bit hardware (both with and without virtual extensions in the hardware), as well as on the new breed of ARM-based servers.  As your datacenter moves forward, your virtualization solution is prepared to move ahead with you.

·         Tool-Agnostic Cloud: The Xen Project was born with the concept that virtualization should be controllable in the manner which later came to be called Cloud Computing.  The availability of Xen Cloud Platform (XCP) and its associated programming interface (XAPI) ensure that you can control your VMs the way you want to, using whatever tool stack you choose.  Cloud technologies such as CloudStack and OpenStack can easily manipulate Xen VMs. There is no such thing as vendor (or project) lock-in to any one cloud solution.

·         Open Source: The Xen Project is now a Collaborative Project of the Linux Foundation, ensuring that the destiny of the project remains squarely with the community.  Yet, the impressive array of commercial project members ensures that substantial resources are marshalled for the continued development of Xen.

·         Moving Forward: The Xen Project continues breaking new ground with incubation projects such as Mirage OS, which will produce certain tiny, highly efficient VMs utilizing exokernel technology.

Clearly, there are lots of reasons to use Xen.  Maybe the better question is, “Why not use Xen?”

Russell Pavlicek is a Xen Project Evangelist who works for Citrix Systems. Introduced to Linux in 1995, he has been an Open Source columnist, speaker, author, and radio personality.



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  • ofr Said:

    I am not convinced. Most of your arguments are very general or applicable to other technologies such as KVM, as well. For instance I think KVM is just as "flexible" or "tool-agnostic" as Xen. Granted, Xen has "pioneered" a lot of stuff, but that's history now, sorry to say. Also KVM works with the ARM architecture now and it's open source. So, as far as I'm concerned, the question remains.

  • Ricardo Said:

    @ofr: Well, if you only compare Xen to KVM there'll surely be much in common. I believe the article is more about comparing Xen with the rest of the hipervisors (VMware, Hyper-V, VirtualBox, etc *and* KVM). If you (re-)read the artcile in that light, you might get a different picture. Cheers.

  • W. Anderson Said:

    I would be curiousd to know if commenter "ofr" has any similar reservation on using Microsoft Hyper-V or VMWare, both of which are strictly "proprietary" with control over any aspect of their development or road map in hands of company that ownes these technologies. While Virtualbox is Free/Open Source Software (FOSS), it is unfortunately under the control of Oracle Corporation, who have a hidious reputation for devestating FOSS projects - much like MySQL and Java.

  • Sum Yung Gai Said:

    I use KVM because it comes with my GNU/Linux distro, and because it works well. However, I've used Xen in the past and have no problem with it, either. Both work well. My chief reasons for moving to KVM were actually somewhat political. When Citrix bought Xen, I wasn't sure if they were going to do like Sun/Oracle and close it down, so when Red Hat bought Qumarnet (sp?) and switched to using KVM (for similar reasons, I'd imagine), I thought, hey, KVM's a Red Hat product now, and Red Hat GPL's virtually everything they write or buy, so this will remain Free Software. Furthermore, the necessary kernel code got included as part of Linus Torvalds's official kernel at, and not just a RH patch (like some other things), so that told me, KVM is here to stay and I can rely on it. Now that Citrix has ceded control of Xen over to an independent foundation, it may be time to take another look at the hypervisor. It's been a few years. --SYG

  • Lennie Said:

    What sets Xen apart from many other hypervisors is Remus, as far as I know only VMware supports something similar. This provides not just High Availability, Fault Tolerance. A form of continuous live-migration. There is some code to get started on implementing it for KVM/Qemu, but I don't think anyone is working on it. There is just to little demand for the feature. What does KVM support better than Xen ? Maybe KVM supports nested hypervisors better than Xen, IBM put a lot of work into that.

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