Today, Microsoft announced the VHD Test Drive Program designed to encourage the company's 7,000 ISV partners to start distributing their wares as preconfigured Microsoft Virtual Server-based virtual appliances.
The VHD acronym refers to virtual hard disk the format Microsoft Virtual PC and Virtual Server use to store their virtual machine (VM) files. It is analogous to the .vmdk format used by VMware. Last month, Microsoft placed the VHD format under a pseudo-open source license called the Open Specification Promise (OSP) license.
VHD appliances are "really cool," said Jim Ni, Microsoft senior technical product manager in the Windows Server group. "If I've got a machine running [Microsoft] virtualization software, I can load the [VHD] image and get it up and running in five minutes," he said.
Furthermore, Ni explained, "the great thing about these VHDs is that they're running in an isolated mode that won't affect other services."
More than twenty Microsoft partners have already committed to distributing software via VHD Test Drive Program by the end of the year, including Altiris, BEA Systems, Check Point, Citrix, CA, CommVault, Dell, FullArmor, HP, Network Appliance, Platespin, Portlock, Quest Software, SourceCode Technology Holdings, Symantec and UGS.
Microsoft's forthcoming Longhorn virtualization platform will also use the VHD format, although it will be different than the VHD format in use today, Ni said. However, Microsoft promises to offer "a clear migration path from Virtual Server to Longhorn virtualization," Ni said, via "tools that make the conversion happen seamlessly." That will ensure that VHD packages created today can still run on the company's forthcoming hypervisor-based virtualization platform.
VMware, for its part, also promotes ISVs to distribute virtual appliances. Last February, the company launched the Ultimate Virtual Appliance Challenge and now boasts more than 300 virtual appliances on its VMTN (VMware Technology Network) site.
Microsoft and Xen, bedfellows
Meanwhile, the full extent of Microsoft's alignment with Linux and Xen for virtualization is starting to make itself felt. Last week, Microsoft and Novell announced an extensive partnership, that, among other things, called for the two companies to collaborate on virtualization technologies.
"We will be developing virtualization technologies together," said Patrick O'Rourke, Microsoft senior product manager in the Windows Server group, including the build-out of a joint lab dedicated to virtualization.
O'Rourke wouldn't specify further what form that collaboration will take, but it stands to reason that it will involve Xen, the open source virtualization project that Novell, with its SUSE Linux, supports.
Xen promises better performance than VMware virtualization by running modified "paravirtualized" guest operating systems. In the past, Xen's use of paravirtualization all but ensured that it would be limited to running Linux -- and not Windows -- guests . To paravirtualize an operating system, "you need access to the source code," explained Tony Iams, vice president and senior analyst with Ideas International in Rye Brook, N.Y., and Microsoft was unlikely to do that.
But the Xen community's commitment to paravirtualization seems to be falling apart. Virtual Iron Software Inc., another virtualization player that relies on Xen, allows users to run any unmodified , non-paravirtualized, operating system provided the physical machine includes virtualization-enhanced processors such as Intel-VT and AMD-v. And today, XenSource Inc. announced that its XenEnterprise, too, would run Windows guests thanks to what it calls "progressive paravirtualization" that inserts paravirtualizing I/O drivers in to a Windows OS.
Could Novell be the next Xen vendor to support Windows guests? Already, this September, Novell announced that it would support not just its own SUSE Linux Enterprise Server (SLES) 10 as a "guest," but also for systems equipped with Intel-VT and the forthcoming AMD-v, unmodified versions of Red Hat Enterprise Linux (RHEL) and older versions of SUSE.
Certainly, the convergence of Microsoft and Linux virtualization seems to be inevitable. Speaking of the VHD Test Drive program, Microsoft's O'Rourke said, "There are no restrictions on what virtualization solutions you can use – it just has to support VHD. Today, Xen doesn't support VHD, but that's not to say that it couldn't."