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Microsoft partners ponder next steps for VHD (virtual hard disk) appliances

Microsoft partners say that VHD-based virtual appliances are useful for test and demonstration purposes, but that the VHD specification will have to evolve for customers to run virtual appliances in production.

LOS ANGELES -- Microsoft's first program to spur creation of Virtual Hard Disk-based appliances is going well, but partners want more out of this good thing. Those attending WinHEC today asked for a number of improvements, including fewer Windows distribution restrictions, VHD (virtual hard disk) format updates and more.

It's been several months since Microsoft announced the formation of its VHD Test Drive program, which gives independent software partners (ISVs) the ability to redistribute Windows operating systems (OSes) within a virtual appliance based on its VHD format. Overall, the company is pleased with its progress.

Speaking on a WinHEC panel devoted to VHDs, Mike Neil, Microsoft general manager for virtualization, said, "We've been very happy with the reception around VHD and the VHD specification. We've seen uptake among all communities – including the open source community – and it's going to be great to see what products come from that."

In addition to Microsoft virtualization software, VHD -- Microsoft's analog to VMware's proprietary VMDK format -- is used as the default virtual machine (VM) format by XenSource and Virtual Iron, while VMware and Parallels virtualization software can also run VHD-based VMs by converting them in to their own formats.

More clients, please
Microsoft partners on the panel also painted a relatively rosy picture of VHD virtual appliances so far. Going forward, though, ISVs want Microsoft to update the VHD format and loosen Windows redistribution restrictions.

Jason Lieblich, CTO at Citrix said the VHD Test Drive program will make it easier for his firm to install complex, interdependent software stacks. "With our customers, it can be tough to get everything properly configured," he said. "As soon as the Test Drive program was announced, we knew we were interested in putting our software together as an appliance." Lieblich said Citrix plans to offer a VHD appliance version of its Citrix Presentation Server (CPS) Platinum Edition this quarter.

But while VHD appliances make it easy for ISVs to put working versions of their software in customers' hands, Microsoft only allows certain Windows Server versions to be redistributed in VHDs, panelists complained.

"We want to get more Microsoft client-based images out to customers in order to give customers test labs that are as close as possible to their environment," said Dmitry Sotnikov, new product research manager at Quest Software, which makes software to manage Windows applications and databases.

Panelists also clamored for the ability to distribute mountable VHDs. Microsoft's Neil said Windows Server Virtualization ("Viridian") includes that feature, and that the company would consider adding in that capability to its current Virtual Server product. "I think we should definitely do that," he said.

VHDs not production-ready
Microsoft's Neil and panelists agreed that there is still a lot of work to be done with the VHD specification.

"We view demonstration environments as a stepping stone," Neil said. "The next logical step is how do you provide production-ready environments?" Complexities include keeping virtual appliances up-to-date with system patches and converting a test environment to production, including licenses.

One way to make VHDs more useful, panelists said, would be to add metadata to the VHD that described its operating system, resource and application requirements. That, in turn, would make virtual appliances easier to update and catalog.

Another useful innovation would be to integrate the VHD format into software development environments, said Dave McCrory, CTO at Inovawave, a virtual machine performance optimization firm that distributes VHDs of virtual appliances running with or without its software, for comparison purposes. "IDEs allow you to test your programs as virtual machines; I want the flexibility to spit it out as a VHD."

The VHD specification is admittedly a moving target, said Microsoft's Neil. As a core disk format in Windows Server 2008 (formerly "Longhorn"), Microsoft is working out VHD's position vis à vis other image formats such as the Composite UI Application Block (CAB) and Windows Imaging (WIM), a packaging format that includes compression, but unlike VHD, cannot be executed. "We're looking at what's different about WIM, and whether we converge WIM's packaging and VHD's runtime abilities."

In short, Neil said, "there are a number of steps we need to take so that applications can run with us." Look for these issues to be resolved in a second version of VHD to ship in the Longhorn timeframe.

Let us know what you think about the story; email: Alex Barrett, News Director.

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