Microsoft Taps Xen to Help Build Longhorn's Hypervisor

Published: July 19, 2006

by Alex Woodie

Microsoft and XenSource announced this week that they will work together on the development of the hypervisor for Windows Server "Longhorn." The odd pairing of XenSource, an advocate of open-source software development, and Microsoft, which in the past has denounced open-source as a threat to intellectual property, shows that Microsoft is serious about ensuring out-of-the-box interoperability of virtualization products.

The partnership between Microsoft and XenSource should benefit both software companies, as well as their customers. For Windows users, the announcement means that the hypervisor layer Microsoft is developing for Longhorn, a product that goes by the codename "Viridian," will support Linux. This hypervisor is due to ship 180 days after Windows Server Longhorn is released to manufacturing (see "Microsoft Unveils 'Viridian' Hypervisor, Extends Virtualization Roadmap").

Microsoft also benefits by gaining the technical expertise of XenSource, which got its start in Cambridge, England, as an open-source software project, and which is now going through the process of trying to commercialize its work. In the past, Microsoft has obtained virtualization expertise through acquisitions, such as its 2003 acquisition of Connectix, which formed the basis of its Virtual Server product. However, Virtual Server's time appears to be short, as the market shifts to more efficient hypervisor layers that sit directly on the hardware, below the operating system layer.

XenSource benefits from the agreement in the short term and over the long haul. In the short term, XenSource gains Microsoft's blessing to support the Windows Server 2003 operating system with the pending release of its hypervisor product, called Xen Enterprise. That product--the company's first commercial offering--is due to ship this quarter. "Longhorn is going to be a formidable and impressive product, but customers that want to get started now have 18 months before Longhorn ships, and can go with a best of breed virtualization ISV," says John Bara, vice president of marketing for Palo Alto, California-based XenSource.

In the long term, XenSource benefits by gaining close access to Microsoft Windows developers as Longhorn is finalized. The company would have supported Longhorn anyway, but now it will be there with support for the operating system on the first day of availability, Bara says. "Instead of XenSource developing Windows capabilities on its own today, in the future, they will be collaboratively developed side by side with Microsoft," Bara says, adding that "whenever you're doing a native mapping with a Microsoft server team, you're going to do things to optimize performance."

From a technical standpoint, the collaborative development agreement between Microsoft and XenSource involves sharing code and swapping APIs. "Basically the two companies will together deliver an interoperability technology, basically a set of adapter and components, to the market as part of the Windows Server Longhorn virtualization product package," Bara says.

The respective "hypercall" APIs for the two companies' hypervisor products will be mapped together so that the Windows hypervisor will be able to run Xen-enabled guests, such as Red Hat Linux and Novell's SuSE Linux. "The XenSource architecture and Windows hypervisor are absolutely aligned after the agreement," he says.

There is also the possibility of running Sun Microsystems' Solaris within the Longhorn hypervisor. Solaris is a Xen-enabled operating system, and it would seem to be technically feasible. Bara says Solaris would be supported, but Microsoft gave a less illuminating response to the question. "We want to extend this commitment and support select non-Windows OSes, specifically, Linux OSes, on Windows Server virtualization technology," a spokesperson said. "Our intent with this agreement is that certain Xen-enabled Linux guests will work in an interoperable manner on Windows Server virtualization technology."

The collaborative union with Microsoft also calls for XenSource to develop a range of add-on products that support Windows over the course of the agreement. The additional products will include "storage, integration, security, and reliability," Bara says. "Those will be add-ons to Xen Enterprise and be interoperable with Windows Server Longhorn."

In this respect, the agreement between XenSource and Microsoft could be viewed as a shot across the bow of EMC and its VMware subsidiary. Analyst groups consider VMware and its ESX Server hypervisor product to be the market-leading forces in the X86 and X64 virtualization market today, and the delivery of add-on products from XenSource for storage, integration, security, and reliability should give it more ammo against EMC, which has already bought VMware, Documentum, and Legato, and is now buying RSA Security.

Terms of the agreement, including the number of years and any financial details, were not disclosed. The work resulting from the collaborative development between the two companies will only find its way into the Xen Enterprise product and will not be extended to XenSource's open-source offerings.

XenSource recently opened an office in Microsoft's hometown of Redmond, Washington, Bara says. That office is staffed by 10 developers who are working closely with Microsoft developers, including Mike Neil, formerly of Connectix who is now heading up Microsoft's virtualization effort in Redmond.

Microsoft says to expect a beta release of the Viridian Windows Server virtualization hypervisor by the end of 2006. Viridian is currently scheduled to be released to manufacturing (RTM) within 180 days of the RTM of Longhorn, which is currently scheduled for the end of 2007.

Bob Muglia, senior vice president of the Server and Tools Business at Microsoft, called the partnership part of a "bridge building" effort. "Microsoft's commitment to customers is to build bridges across the industry with solutions that are interoperable by design," he says.

Microsoft's tone has shifted not-so-subtly from the near past, when it has railed against the open-source software model and the lack of strong indemnification against intellectual property lawsuits. For example, in January 2005, Microsoft CEO Steve Ballmer put the Linux community on edge when he declared that Linux infringes on 228 patents and that "someday . . . somebody will come and look for money owing to the rights for that intellectual property."

Now, Microsoft is committed to "building bridges" with the Linux and the open-source community through XenSource. Hopefully, it will keep building bridges with other parts of the open-source community as well.

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