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Windows Server Virtualization Preview

Microsoft this week shipped the Release Candidate 0 (RC0, and no I don't understand the naming convention either) version of Windows Server 2008, allowing customers to get their hands on near-final code of the upcoming OS for the first time. Windows Server 2008 RC0 doesn't differ much from a functional perspective from the previous release, a June 2007 Community Technical Preview (CTP) release (see my Windows Server 2008: Need to Know showcase for more information). But it does come with one major new feature: The first public pre-release version of Windows Server Virtualization (WSV), codenamed Viridian.

A look at Microsoft's virtualization technologies

If you're not familiar with Viridian, it's helpful to understand where Microsoft's virtualization solutions stand today. Currently, Microsoft offers a free server product called Virtual Server (and an accompanying free desktop product, Virtual PC) that provide traditional (i.e. user mode) virtualization environments. Virtual Server could very well be the pinnacle of this type of technology, at least from Microsoft, given that it will be obsolete as soon as the more performant, maintainable, and efficient WSV arrives next year. For those looking ahead to this future, Virtual Server's Virtual Hard Drive- (VHD-) based virtual machines will work fine--if not quite a bit better-if and when you later upgrade to Windows 2008 with WSV.

On the management side, Microsoft offers Virtual Machine Manager, an enterprise-class virtual machine management solution that's currently aimed at Virtual Server customers but will be updated for WSV once that technology becomes available. VMM extends the basic capabilities of Virtual Server management, which is generally designed for managing the virtual machines on a single physical server, into a more scalable solution. VMM offers centralized virtual machine management across hundreds or thousands of physical machines, and can handle thousands, or even hundreds of thousands of virtual machines.

VMM automates many crucial tasks. For example, virtual machines that are running out of resources on one physical machine can be automatically relocated to new hardware with minimal disruption and end user transparency. VMM also provides for physical to virtual (P2V) conversions, as well as virtual to virtual (V2V) conversions of VMware virtual machines to Microsoft virtual machines. (And say what you will, but that last feature should prove quite popular.)

Unlike Virtual Server (and the upcoming WSV), VMM is not free, but given its expansive feature set this is somewhat unsurprising. You can get into VMM as cheaply as $499 for a version that can manage up to 5 physical host servers. Beyond that, you're in volume licensing territory.

Enter Viridian

This week, I'm excited to finally be able to provide more detail about Windows Server Virtualization, as this is a technology that we've all been waiting to get some hands-on time with. Here's what I know so far.

Bryon Surace, a program manager in Microsoft's Virtualization team told me in a briefing earlier this month that the overall schedule for WSV hasn't changed. The company still intends to ship a beta version of WSV when Windows Server 2008 is completed in the first quarter of 2008. What they've shipped this week is a pre-beta, or alpha, version of the technology that is essentially feature-complete. It is not, however, extensively tested, so you shouldn't expect to use WSV anywhere near production servers. Even the branding for WSV is still in play: While Microsoft might use the WSV name for the final version of the product, it is considering other options.

"The big issue here is that Viridian is a component of Windows Server 2008 and not a separate product like Virtual Server," Surace told me. "It's a brand new architecture based on the Windows Hypervisor. From a management perspective, Viridian is installed and managed as a role under Windows 2008, just like DHCP, file and print services, and so on."

Contrary to some reports, WSV can be installed on either a Server Core install of Windows 2008 or a more traditional install of the product. That said, Microsoft strongly recommends that any future live deployments of the technology should occur on Server Core, because that type of near-bare-metal install type will provide a smaller attack surface and better performance. So while the company will support WSV installs on traditional Windows 2008 servers, it is essentially providing that option mostly for testing purposes.

Another issue to consider is the underlying hardware. Though Windows 2008 will ship in both 32-bit (x86) and 64-bit (x64) variants (as well as some versions for the Itanium platform), WSV will be available only on x64 versions of the product. (And while the specific product versions haven't yet been locked down, Surace tells me that WSV will be an option on all x64 versions of Windows 2008, and not limited to certain versions.) The reason for this limitation is that WSV relies on hardware virtualization features that are only available in the latest AMD and Intel chipsets.

WSV will support both 32-bit and 64-bit guest operating systems, which in WSV parlance run in child partitions. (The host OS runs in the so-called parent partition.) It will support up to 32 GB of RAM in each guest OS, a huge improvement over the 3.6 GB limit in Virtual Server 2005. WSV will also support allocating up to 4 physical CPU cores to each guest OS.

Aside from the underlying architectural differences, the big difference between WSV and Virtual Server, and indeed, other virtual machine platforms like those provided by VMWare, is that WSV supports the notion of virtualized, or synthesized, devices. In other systems, the hardware that's "seen" by each guest OS is emulated, which makes for decent compatibility but poor performance, Surace said. WSV's synthetic device drivers improve performance by dramatically reducing the number of traversals the system needs to make between kernel mode and user mode.

"This is a new approach that removes the performance bottleneck," Surace told me. "We call it OS enlightenment: The OS knows it is using synthesized device drivers and knows that it's being virtualized. It's similar to the para-virtualization scheme in Xen [an open source virtualization engine]." Enlightened OSes include Windows Server 2003 and 2008, and Microsoft is partnering with Xensource to ship drivers for Linux so that Linux, too, can be "enlightened."

Installing WSV on Windows Server 2008 RC0

If you navigate into Add Roles in Server Manager in Windows Server 2008 RC0, you won't actually see a Windows Server virtualization role. This is by design: Microsoft didn't want testers to casually install this option by mistake, because it isn't as fully tested as the rest of the product. In order to enable the ability to add the Windows Server virtualization role, then, you'll need to run two executables in the C:\Windows\WSV folder. They both install in about 30 seconds, and once that's complete, and you've rebooted the server, you'll see Virtualization show up in Add Roles.

This reboot is required because WSV changes the underlying architecture of the server in fairly dramatic ways. "Conceptually, it jacks up the OS and slides in the Hypervisor underneath," Surace told me. "So we clearly don't want that installed by default on servers that won't be running Virtualization. But it's that simple to get it installed."

Once WSV is installed, as is the new Virtualization role, you'll notice some not so subtle changes if you're familiar with Virtual Server: Microsoft has replaced the Web-based management interface from that product with a true Microsoft Management Console (MMC) interface. This makes sense: Since WSV is an integrated component of Windows 2008, it is managed in a manner that's similar to other WSV components.

Comparing WSV and VMM

Compared to the aforementioned Virtual Machine Manager product, WSV management is simpler and less scalable, because the assumption is that those using the WSV management interface will typically be managing a single server, or a small number of servers. VMM, meanwhile, scales up to hundreds or thousands of servers, which could have tens of thousands of virtual machines configured on them. VMM also provides unique features for the larger environments it targets, like machine migration and orchestration, triggering, and alerting.

While the current version of VMM is not compatible with WSV, a future version of VMM will be. Microsoft intends to ship this new VMM version at the same time as WSV, and will likely ship a beta version to coincide with the first beta of WSV in the first quarter of 2008.

Looking ahead

Once I've had some hands-on time with the WSV preview, I will provide more information on this site. For now, you should understand that the existing code hasn't been thoroughly tested, so there will be bugs, particularly in the Quick Migration feature. That said, I'm excited that Microsoft has chosen to provide a version of this software that is near feature complete: Given the relative silence and dearth of details about this product over the past several months, this release is like a sudden and bright burst of sunshine on a cloudy day. Is Viridian the virtualization platform of the future? We're about to find out.

This article is an expanded combination of my commentaries from the September 11, 2007 and September 25, 2007 issues of Windows IT Pro UPDATE. --Paul

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