Microsoft this week is scheduled to take its first step into server virtualization with the release of Virtual Server 2005, but the company will face a rash of technological, licensing and support challenges before it can claim success.Microsoft\u00a0this week is scheduled to take its first step into server virtualization with the release of Virtual Server 2005, but the company will face a rash of technological, licensing and support challenges before it can claim success.Corporate users are aware that\u00a0Virtual Server 2005, which lets multiple operating systems run on a single physical machine, is heavily Windows-centric and lacks the performance capabilities and feature set of other virtualization architectures.In addition, Microsoft's software licensing has not been altered to accommodate virtualization - leaving users with savings on hardware when consolidating servers but not on software.Also questions are arising about Microsoft's plan to support Windows operating systems when they are running on Virtual Server 2005 but to deny support when those same operating systems run on another vendor's virtual machine technology."One of our concerns is the Microsoft product will be very Microsoft-specific," says Allan Campbell, director of IT architecture for MassMutual Financial Group in Springfield, Mass. "We are looking at Linux and we want our virtualization strategy to support that, and so we are concerned about Microsoft's real commitment to supporting Linux on their virtual platform."Virtual Server 2005, which requires Windows Server 2003 as the "host" operating system under Virtual Server, supports\u00a0Linux\u00a0as a "guest" operating system running inside a virtual machine, but Windows NT and 2000 are the featured guest operating systems."There are optimizations that we will do to make sure that Windows performs the best in that guest environment so that we can actually tune it for a virtual machine environment," says Eric Berg, group product manager for Windows Server. "And you can expect to see slower performance on those operating systems that are not tuned for that environment."That deference to Windows, in part, is why Campbell is using VMWare's\u00a0ESX virtualization platform\u00a0to consolidate roughly 80 Windows servers onto four eight-way IBM servers. Microsoft's support policy is the reason Campbell almost exclusively uses those virtual machines for testing and development, and not in production."VMWare is not an officially supported platform for Microsoft," Campbell says. "If we have a problem with the Windows software they don't have to give us support unless we can recreate the problem on a physical server."The support issue is different with Virtual Server 2005 - Microsoft will support versions of Windows that run on virtual machines, according to Microsoft's Berg.Campbell says he is pleased Microsoft is taking virtualization seriously but that the company will have to answer licensing and support questions.Microsoft has not altered its licensing and the company says it doesn't plan to do so in the near future, leaving users to pay for each server within each virtual machine.In fact, license pricing is an industry-wide concern.\u00a0Novell\u00a0and\u00a0IBM\u00a0license SuSE Linux and AIX, respectively, per server and not per virtual machine.\u00a0Red Hat Linux\u00a0licenses its software per virtual machine."Licensing software for a static entity is the old way of doing things," says Gordon Haff, an analyst with Illuminata. "That won't be acceptable going forward and won't correspond to how users are running applications and systems using virtualization."In addition to those lingering issues, users have technology hurdles to clear.Peter Sellers, analyst for desktop LAN engineering at DTE Energy in Detroit, has been testing Virtual Server for a year and likes the technology but is stymied by two features: support for the Virtual Network Computing protocol for remote access and the requirement to run Microsoft's Internet Information Server to support Web-based access to Virtual Server."Both are prohibited on our network," Sellers says. "I'd rather have a console for Virtual Server and forgo the Web-based management. That would eliminate one big hurdle for us."Virtual Server also requires Win 2003, while competitors such as VMWare's\u00a0GSX\u00a0and\u00a0SW-Soft Virtuozzo\u00a0provide a Win 2000 or Linux option for the host operating system. VMWare's ESX bypasses the host operating system altogether with a technology called Hypervisor, an optimized operating system or microkernel, built into the virtualization platform. ESX also supports virtual machines across multi-processors, while GSX and Virtual Server support only single-processor deployment."If you are serious about doing virtualization as an IT strategy, the microkernel-based approach is really the best approach because you don't have a big fat host [operating system] as a security attack target," says Michael Mullany, vice president of VMWare.Microsoft officials don't dispute the performance improvements with Hypervisor but say Windows Server 2003 as the host operating system provides a consistent driver model so users don't have to worry about device compatibility.It fits into Microsoft's overall strategy for virtualization, experts say."The Microsoft strategy is a migration strategy, while VMWare is a consolidation strategy," says Dan Kusnetzky, an analyst with IDC. "Microsoft is focusing on how do we offer a Microsoft-centric virtualized environment that allows multiple Microsoft stacks of software to run on the same machine either for consolidation, legacy applications or separation of workloads. Other operating environments are secondary. Microsoft's view is that this technology is largely a way to help people who are on older versions of software move to the newer ones."