Microsoft opens up VHD

Posted on 17 Oct 2006 at 18:16

Microsoft has said it is to release its Virtual Hard Disk (VHD) format under its newly minted Open Specification Promise (OSP).

The move is potentially a major step forward in interoperability between open-source and Microsoft's implementation of virtualisation.

The Virtual Hard Disk is a means of capturing the operating system and application stack of a virtual machine in a single file.

It was already licensed royalty-free to third-party developers, as it is one of the cornerstones to Microsoft's roadmap for virtualisation. However, Microsoft's royalty-free licences have not so far been compatible with open-source technologies because of licensing issues.

Open-source virtualisation company XenSource's CTO Simon Crosby, told us that previously its customers would have to license Microsoft's VHD separately to any open-source implementation of virtualisation as 'VHD cannot be implemented in open source'.

Leigh Day, Director of Corporate Communications at Red Hat told us that 'VHD is a proprietary technology and differs from the Red Hat approach which is to offer customers an open, standards-based, integrated, platform. Customers who choose Linux do so because of the value of open standards and collaboration. VHD is neither open nor developed and improved collaboratively, so support for this technology is not on Red Hat's near term plans as part of our Integrated Virtualization strategy.'

However, Microsoft's announcement of its OSP, which offers royalty-free licensing, and includes a promise 'not to assert any Microsoft Necessary Claims against you for making, using, selling, offering for sale, importing or distributing any implementation to the extent it conforms to a Covered Specification ("Covered Implementation"),' is pretty much number one of one Microsoft announcements welcomed by the open-source community.

Endorsements rained in from such luminaries as Lawrence Rosen and Andrew Updegrove, lawyers specialising in open-source issues, and Mark Webbink, Deputy General Counsel for Red Hat.

And far from Microsoft firefighting Linux and open-source with its Get the Facts campaign, it now talks warmly and openly about open-source - and its customers.

'We are focused on delivering interoperability by design,' said Bob Muglia, senior vice president of the Server and Tools Business at Microsoft. 'This means that customers have control over their data while vendors provide technologies that connect diverse systems. By having the VHD specification available under the OSP, the technology is viable for any development or business model. We continue to increase our commitment to interoperability in our products and by providing access to technologies like the virtualization open format.'

Despite this, Microsoft is some way behind its open-source counterparts in terms of delivering on a virtualisation strategy. XenSource's virtualisation platform already supports the higher performing modified, or para-virtualised, versions of Linux distributions, whereas Windows XP can only run as a guest operating system.

A Novell spokesperson told us: 'We like the fact that at some point in the future our para-virtualized SUSE Linux Enterprise Server 10 will be capable of running on top of a Microsoft Windows Server. This opens new options and flexibility to our customers - when it eventually ships.

'To our knowledge Microsoft has not announced that it will modify Windows to run as a virtualized operating system running on top of a Linux server. We cannot obviously modify Windows to make it paravirtualized, because Windows is closed source and proprietary code. Thus, the only option for a customer is to run unmodified Windows using hardware-based virtualization with Intel VT or AMD-V. And right now, the only operating system that enables you to do that is SUSE Linux Enterprise 10.