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Xen-based virtualization minimizes hypervisor relevance

From XenServer to Sun xVM, Xen-based products have challenged VMware's market share and deemed hypervisor technology less relevant. Lower pricing, better packaging and less emphasis on hypervisors may spell long-term success for Xen.

VMware Inc. would like everyone to believe that it is the unquestioned champion of the virtualization war. Unfortunately for VMware, an armistice has yet to be decreed, and the lower prices of Xen-based platforms will spur new battles.

Lower-priced rebel virtualization platforms built on the Xen hypervisor have the power to take on VMware Infrastructure (VI). This article considers two of them: Citrix Systems Inc.'s XenServer and Sun Microsystems' Sun xVM. Both Citrix and Sun have challenged VMware's dominance by subtly offering Xen as part of complete, vertical and, most important, inexpensive packages. I'll reveal some of their strategies to usurp the throne from the would-be virtualization monarch and make a prediction on the ultimate legacy of the Xen hypervisor.

Virtualization with Citrix XenServer
In the months following last August's announcement, Citrix's virtualization strategy with the newly acquired XenServer became increasingly clear. Citrix has seamlessly blended the Xen hypervisor into its product line with XenApp, XenDesktop and XenServer.

The new XenServer product line takes advantage of multiple virtualization areas. First there is XenApp, a re-imagining and re-branding of Citrix Presentation Server. XenApp is the premier software product for delivery applications to users. But why serve just applications when you can offer the entire desktop? XenDesktop is Citrix's foray into remote desktop delivery, or its version of VMware's Virtual Desktop Infrastructure (VDI).

Underneath it all is XenServer, a Xen-powered hypervisor capable of hosting XenApp and serving up virtual desktops for XenDesktop. With this software stack, Citrix has asserted the notion that it's not the hypervisor that matters, but rather what you can achieve with it. And achieved Ctirix has: Citrix offers a complete, proven technology to IT departments that need to consolidate desktops and software into data centers.

VMware has just reached beta two of its Project Northstar (formerly known as Thinstall), and its Virtual Desktop Manager (VDM) broker has just become enterprise-ready in its latest release (version 2). Microsoft's acquisition of Softricity (which became Microsoft SoftGrid, which is now Microsoft Application Virtualization), enables Microsoft to compete directly with Citrix XenApp, but the technology is not as proven as Citrix's Presentation Server. And Microsoft Hyper-V still isn't generally available. As it stands now, if you want to bring desktop and application delivery into your data center, Citrix holds the keys to the most proven technology out there. And it is all powered by the little hypervisor that could: Xen.

Sun's xVM Server
Sun xVM Server is Sun's first attempt at a no-operating system virtualization architecture. Solaris Zones (now known as Solaris Containers) were a well-liked addition to Solaris, but the feedback I've gotten from many systems administrators was that patching and container management was too difficult. For about three years, Sun has worked to integrate Xen and Solaris, culminating in Sun xVM Server.

What is the significance of Sun xVM Server? Simply put, if Sun manages to acquire or develop an application virtualization/delivery technology, it will be poised to have the most complete virtualization technology available. Through Sun, IT administrators will be able to procure Sun servers, a hypervisor (xVM Server), desktop delivery software (Sun Desktop Infrastructure) and, most important, management software that can manage the OS, the hypervisor and the hardware (Sun xVM OpsCenter). Currently, if you are searching for a virtualization technology (though one without application delivery), Sun offers a top-to-bottom option.

Citrix and Sun's Xen-based strategies
Packaging and price will offer Citrix and Sun an advantage in the virtualization marketplace.

Reducing cost is the order of the day, but many observors firmly believe that you get what you pay for. Many think that because VMware's product is the most expensive it must be the best. I am not arguing that it is or isn't. But a large population of IT managers seem to think that if a product is free, it is too good to be true. Does a price somewhere in the middle have market appeal? Citrix XenServer Enterprise is priced at $2,600 for a perpetual license. Sun xVM Server is not yet priced, but Sun's xVM Ops sales team promised to provide me with that information as soon as it is available so look for an update soon. I expect Sun's pricing to be comparable, if not less expensive. to Citrix XenServer, as the later-to-market product usually reduces price in order to gain a foothold. Compare this to VMware Infrastructure at $5,750. Note that none of the prices mentioned reflect optional software assurance agreements. One of most flexible aspects of IT is pricing, but the difference in cost between VMware and Xen remains substantial.

By making the hypervisor invisible, Xen vendors hope to upstage VMware. They realize that in an end-to-end technology, the hypervisor -- whether it is VMware ESX or Xen -- is irrelevant. If VMware hopes to survive, it must continue to build its IHV partnerships and downplay the role of the hypervisor among the virtues of its technologies.

The legacy of Xen
Although this article discusses only two Xen-based hypervisor products, there are several others, including those made by Oracle Corp., Virtual Iron Software Inc., Red Hat Inc. and others. The ubiquity of the Xen hypervisor may be its ultimate legacy. Much like Java, despite clear advantages over competitors in the same space, Xen will never be the face of an entire industry. Instead, it is fated to exist as a permanent fixture in the virtualization space. Xen is destined to become the go-to hypervisor for use in embedded servers, Linux operating systems and enterprise application vendors. We may eventually see OEM hardware shipping with stickers on the bezels announcing "Xen Inside."

About the author: Andrew Kutz is a leading expert on x86 server virtualization, specializing in VMware ESX and the VMware Infrastructure (VI) Software Development Kit (SDK). Kutz is currently working on a book for O'Reilly Associates titled Programming and Managing VMware Infrastructure. He is also the author of the popular open source project Sudo for Windows (sudowin) and the VI client plug-in SVMotion. Kutz works for the University of Texas at Austin as a senior systems analyst. He lives in Austin with his wife, Mandy, and their four daschunds.

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