A Primer On Microsoft's New Hyper-V

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New technology allows for closer interoperability between Windows and Linux than we've seen in the past, and also puts it at loggerheads with technology offered by VMware, whose virtualization technology has been taking the industry by storm.

The early release of Windows Server 2008's Hyper-V Beta signals that Microsoft is well ahead of schedule in a key area of development. But that's no big surprise: Hyper-V technology started with the Xen source code, so the company had a big head start.

Microsoft partially funded the Xen project, which suggests why the beta release supports Linux interoperability. The Redmond, Wash., industry giant plans to support some enterprise Linux distros in the long term—the first one being SUSE Enterprise 10 with SP1. Fedora Core 8 now works with Hyper-V.

To expand its integration capabilities with other Linux distros, the Windows Server 2008 group is opening up a testing program through Microsoft Connect's site. (Solution providers have to apply to get into the testing program.)

Xen shares a communication layer with Hyper-V. Hyper-V provides components for a synthetic network adapter, synthetic storage controller and Xen's Hypercall adapter. When running a Linux virtual machine, Xen calls are translated into Hyper-V hypercalls. Though the Xen hypervisor runs in Ring 0, it still has to communicate with Hyper-V.

The Hyper-V layer will execute instructions at the lowest service provided by Windows Server 2008. The Hyper-V layer requires a root-level partition to run, so the Windows Server 2008 kernel is treated almost equally with other Windows and non-Windows kernels. "Almost equal" means that Windows Server 2008 will be the constant in the new architecture.

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Hyper-V comes as an integrated service in Windows Server 2008, so it is not a hosted platform. The integration gives Microsoft a huge advantage over VMware because customers can get two products for the price of one. A fight for data center supremacy might emerge out of this technology. Windows and Linux are no longer on equal footing due to Hyper-V's low-level control over kernels and competing hypervisors.

However, few versions of Windows Server 2008 Standard and Enterprise do not require Hyper-V, so Microsoft must tread carefully to not impede other hypervisors and open source OSes from competing with its virtualization technology and new server OS, respectively.

From Hyper-V's standpoint, Windows and Linux guest OSes are able to control hardware devices on their own. For instance, Hyper-Vs can receive instructions from guest OSes to perform hardware reboots. In addition to power states, other hardware properties, including resources, are available programmatically.

Microsoft is following its Open Specification Promise—a covenant with the industry to provide documentation on how some of its technology works. As such, it has provided a document detailing all the interfaces and CPU register accesses available in Hyper-V. The document allows developers to develop compatible hypervisors. The information provided is high level, however, and does not follow standard documentation format.

In addition to the hypervisor, Microsoft is providing a list of its enterprise middleware that can be tested in Hyper-V. Products such as BizTalk Server 2006, Exchange Server 2007 SP1, Office Sharepoint Server 2007 and many others conform to Hyper-V's virtual hard disk (VHD) format and are available as preconfigured VHD packages. Partners like Citrix Systems, Quest Software and SplendidCRM are providing package solutions using the VHD format. For now, Microsoft is staying with the VHD file format that was available back in 2005 with Virtual PC 2004.

But there's more to virtualization than hypervisor technology. Managing virtual domains in large data centers requires sophisticated tools. VMware, based in Palo Alto, Calif., offers a wealth of enterprise management tools and so does its partner community. XenSource, also in Palo Alto, recently shifted its product line to better align itself with large data centers. Other than VMware and XenSource, other hosted virtualization platforms will probably not be able to compete head on with Windows Server 2008.

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At press time, Microsoft had released a list of eight servers that support the current Hyper-V Beta (see box at right), and additional servers that could be deployed, but on which Microsoft offers no guarantees. The CMP Channel Test Center had difficulty installing the OS with Hyper-V on Hewlett-Packard's Proliant DL360 G5 and on SuperMicro's newest Intel-based Stoakley server. The Proliant server was approved to work with Hyper-V. The Stoakley server is still a work in progress.

Other servers with similar chipsets might actually work as long as the servers include embedded virtualization. Once the OS is installed, a single command-line step starts the Hyper-V installation. Managing Hyper-V's state from the command line is just as easy.

However, the Test Center is continuing to examine the software and its specifications to determine the exact hardware requirements that will satisfy the installation on additional servers. That information has not been supplied by Microsoft.

The initial test with the beta was limited to running only one virtual SCSI and one virtual network controller. This is sufficient to test a virtual machine but not to scale it. High availability is supported in the beta.

Hyper-V's core works outside the device driver layer so it can be made highly secure, since it only creates isolated partitions. The steps to get the service up and running are simple:

1. Install the server software;
2. Open the management console;
3. Choose the option to start a new virtual machine.

As the name Hyper-V implies, Microsoft is providing basic virtualization and management support in Windows Server 2008. The Test Center—like engineers throughout the industry—is in the process of testing the technology. More details will emerge on Hyper-V, the new Virtualization Management Console and other key Windows Server 2008 services.