Microsoft to Distribute VHD Spec Under New OSP License

Published: October 18, 2006

by Alex Woodie

Microsoft yesterday added one more item to its list of technologies that it's putting out into the open source world. By committing to distribute its Virtual Hard Disk (VHD) technology under its new Open Specification Promise (OSP) license, which it introduced last month as a way to foster the adoption of Web services specifications it developed, both customers and developers of virtualization software will benefit from increased interoperability and security, the software giant says. But some virtualization vendors wonder if Microsoft is doing as much as it could for interoperability.

The VHD format, which was first introduced in May 2005, is a key element in Microsoft's virtualization product stack, both now and in the future. The format enables the entire virtual machine operating system and the application stack to be captured in a single file, which makes it easier for applications and data contained in a virtualized environments to be moved among guest and host systems. It's used in the Virtual PC 2004 and Virtual Server 2005 products now available, and will be used in the new hypervisor layer that open source virtualization developer XenSource is helping Microsoft build for the upcoming release of Windows Server "Longhorn."

Microsoft says more than 60 partners have already licensed the VHD format, which has been available under a royalty-free license since it became available last year. The list includes Brocade Communications Systems, BMC Software, Diskeeper, Network Appliance, and Fujitsu-Siemens, Virtual Iron, and XenSource.

OSP Licensing

Yesterday's announcement is as much about how Microsoft interoperates with the open source community as it is the future of VHD and virtualization technology.

Microsoft's royalty-free licensing scheme has been a source of concern for many backers of open source software development. While the developers could get their hands on key Microsoft technologies using royalty-free licensing, they didn't feel safe in adopting the technology under Microsoft's terms, and were afraid that Microsoft might choose to sue them if it didn't like how they adopted the technology.

This is why Microsoft developed the OSP license last month. With the OSP, Microsoft is making a legally binding commitment not to sue people or organizations that adopt patented technologies distributed under the OSP license. "Microsoft irrevocably promises not to assert any . . . claims against you for making, using, selling, offering for sale, importing, or distributing any implementation . . . " the company says on its Open Specification Promise Web page.

When it launched the OSP program last month, it also placed 35 Web services specifications under the licensing scheme, including eight WS-Security specs, WS-MetadataExchange, the Web Single Sign-On Interoperability Profile, its upcoming "InfoCard" identity management technology, and many others. Now the VHD spec has been added, too.

Microsoft could have adopted one of the existing open source licensing schemes instead of the OSP program. Call it "The Microsoft Way," but it already has the backing of two open source bigwigs for its new OSP program, including Red Hat and Lawrence Rosen, a leading technology lawyer.

Microsoft is banking on a similar reaction from the open source community for its new VHD licensing plans. Simon Crosby, chief technology officer of XenSource, says his company is happy to be working with Microsoft. "Today, we use Microsoft's VHD format to consume virtual machines that are created in Microsoft Virtual Server and get them up and running on XenEnterprise. Longer term, we're jointly developing technology so that Xen-enabled Linux guests will run on Windows Server virtualization when it becomes available with the future version of Windows Server, code-named 'Longhorn.'"

Similarly, Jens-Peter Seick, vice president at Fujitsu Siemens Computers, sees the move opening up use of VHD. "VHD will certainly set an important new standard in the area of server virtualization," Seick says. "A common virtualization format like VHD helps provide more seamless manageability, security, reliability, and cost-efficiency for customers, and it helps ensure a uniform product support system."

A Virtualization Standard?

VMware, a subsidiary of EMC and the dominant vendor in the virtualization space, is not completely impressed with Microsoft's moves, which is not completely surprising. The company, which put its own virtual file format, called Virtual Machine Disk Format (VMDK), out into the open source world earlier this year, doesn't plan to adopt VHD.

"It's a good move in that Microsoft is adding openness to their language," says Dan Chu, senior director developer and ISV products at VMware. "In a very narrow sense, it's a big improvement."

However, at the same time it's opened the VHD spec for anybody to use, Microsoft has also added "extremely restrictive language" to VHD use agreements, Chu says. "It seems to completely undercut any potential interoperability, which would be the main reason to make this open," he says. "They've replaced one choke point with another."

Chu says that what really needs to happen is for virtualized file formats to become an open standard governed by an independent body. "These formats should be completely open," Chu says. "We believe that this should move to standards body."

Such a move is not completely out of the question. Last week, Microsoft committed to submitting its new XML Paper Specification (XPS) format to a standards body, although it has not yet done so. The move was one of several by the software giant to appease the European Commission and the EC's stance on Windows Vista (see the story "Microsoft Abides by EC Requests on Vista" in this issue of The Windows Observer).

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