Microsoft’s Virtual Server 2005 R2 is built along the same lines as VMware but requires Windows Server 2003 as the host OS and, unlike VMware ESX Server, it cannot run in a bare-metal scenario. The latest release adds a fairly nifty Web UI and support for Linux VMs (virtual machines); it is also available as a free download.

Microsoft is also preparing Virtual Machine Manager, a virtualization management tool based on Virtual Server 2005 R2. Currently in beta, Microsoft is planning a full release of Virtual Machine Manager later in the year.

In spite of all this, Microsoft faces an uphill battle, and these new products may be delivering too little, too late. In preliminary testing, Virtual Server 2005 R2 functions well, but is dogged by performance issues seemingly related to I/O bottlenecks. Further, the x64 version that runs on Windows Server 2003 x64 for the AMD Opteron and Intel EM64T processors actually runs as a 32-bit application in WoW (Windows on Windows), which further hobbles the performance on those architectures.

In a display of classic Microsoft thinking, all the Virtual Server management tools require Windows and Internet Explorer 6.0 or later, and all VM console interaction is handled via an ActiveX control embedded in a browser window. The Web GUI is nicely laid out, but can be quirky at times, requiring too much effort to accomplish seemingly simple tasks such as mapping an ISO image to a VM CD-ROM drive.

Virtual Server’s management tools are lacking when compared to other players in the x86 virtualization market, but Microsoft recently announced System Center Virtual Machine Manager, which is being built not only to manage Virtual Server, but also to provide a management framework for the Windows Server Virtualization services that will be built into Longhorn.

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Virtual Machine Manager has a similar purpose as VMware VirtualCenter, with a few additional features. It includes Microsoft’s take on physical-to-virtual migration tools -- limited to Windows servers -- and it borrows from Volume Shadow Copy to perform block-level server migrations. Also included are a variety of consolidation tools that can inspect a physical datacenter and propose a virtualization migration strategy based on performance and resource utilization metrics.

All of these tools leverage existing Microsoft technologies such as Active Directory to get the job done, which is a benefit in a Windows-centric infrastructure. But although Virtual Server now supports Linux guest OSes, Microsoft is not going so far as to support Linux with its management tools, preferring to let third-party ISVs handle that piece of the puzzle.

Microsoft expects to ship a hypervisor for Longhorn Server within three months or so of the initial release of the OS, and has promised that closer ties to the OS kernel will result in better virtualization performance. If true, then the stand-alone Virtual Server product will likely become a thing of the past; all the functionality it currently provides will become a standard server role, much like a domain controller or application server. On the other hand, if Longhorn fails to remedy sluggish VM performance, Microsoft may continue to lag at the back of the virtualization pack.