Virtual unrealities exposed

Who are the main companies providing virtualisation technology and what are there different strategies?

1. VMware: The old hand
VMware dominates virtualisation for x86 systems, and more or less invented the market others are now trying to cash in on. Three of its core products are VMware Workstation and the freely available VMware Server (formerly GSX Server) and VMware Player. The software runs on Windows or Linux.

Workstation is designed for applications such as software development and testing, while Server is targeted at the data centre, for uses such as testing patches, simplifying provisioning and using virtual appliances. VMware Server was released in July, replacing ESX Server. VMware Player runs virtual machines created by other applications — including Microsoft's VirtualPC — but can't create its own.

Those products need a host operating system to run on, while VMware's flagship ESX Server drastically increases performance by eliminating the need for a host. Instead, ESX uses its own stripped-down kernel, and runs on bare-metal servers. The approach allows support for more guest virtual machines, but the ESX kernel doesn't have as broad support for hardware.

VMware Infrastructure 3, released in June, includes ESX Server, VirtualCenter management tools, Virtual SMP (symmetric multi-processing) up to four-way, VMotion, VMFS distributed file system software, and new tools such as Distributed Resource Scheduler and High Availability and Consolidated Backup. VMotion allows guest virtual machines to be transferred from one physical system to another without interruption, and can be used for things such as hardware maintenance and load balancing.

"Companies are no longer treating servers as a single entity, they're treating them as part of a giant resource pool," says VMware's Raghuram.

Competitors such as Microsoft and Xen may have achieved a significant foothold in the types of services provided by VMware Server and VMware Workstation, but may not be able to offer anything comparable to the mature administration tools of VirtualCenter for some time. "The ambitions of people like Microsoft and Xen go beyond basic virtualisation, but they have a long way to go," says Raghuram.

2. Microsoft: Grabbing a slice
Microsoft offers Virtual PC — acquired along with Connectix — as its desktop virtualisation tool for Macintosh and Windows. Virtual Server, which requires Windows Server 2003, was also developed by Connectix, but hadn't yet been released when the company was acquired.

Virtual Server 2005 R2, the latest version, introduces support for Linux guest operating systems, the ability to make use of (but not virtualise) SMP, support for x86-64 hosts (but not guests), and a redesigned Web administration interface. Virtual Server needs a host OS, unlike VMware's ESX Server or XenSource's Xen Enterprise, meaning significant processing power overhead.

Virtual Server has been demonstrated with support for Intel's VT and AMD's SVM, which will be included in the next release. Microsoft is currently beta-testing Service Pack 1 for Virtual Server 2005 R2, with a Beta 2 scheduled for Q4 2006. Also in development is System Center Virtual Machine Manager, Microsoft's answer to VMware's VirtualCenter, with a release scheduled for this year. The tools will only support Windows guest OSs, leaving Linux support to third parties. In a classic case of Microsoft's thinking on integration, all of Virtual Server's administration tools require technologies like Internet Explorer and Active Directory.

As of April 2006, Virtual Server is available free of charge. Microsoft also made Virtual PC a free download in July, at the same time announcing a that Windows Vista Enterprise's licensing terms will allow customers to install up to four virtual copies of the OS for a single user on a single device. The licence doesn't require use of Microsoft's technology to create the virtual machine.

Most importantly, Longhorn Server — currently scheduled for 2007 — will get a built-in hypervisor (code-named Viridian) within about three months of release. The strategy is clear: virtualisation, in Microsoft's world at least, will become an operating system feature, just as the Web browser did.

Reviewers have not been overly impressed with Virtual Server so far, but Microsoft believes it's good enough for most uses. "Some customers have niche requirements that might require niche products," says Alfred Biehler, Microsoft UK product manager for management and virtualisation. "For the majority of the market, we believe we've got a good solution. And it will just get better." Microsoft also argues there's an advantage in having the entire operating system and virtualisation stack supported by a single vendor.

Microsoft has been paying attention to interoperability issues, say competitors such as Xen. Viridian will use paravirtualisation, and architecturally is very similar to Xen, which should make interoperability easier, according to Simon Crosby, chief technology officer at XenSource.

In June 2005 Microsoft made the specification for the Virtual Hard Disk (VHD) image format (used by Virtual PC 2004 and Virtual Server 2005) available under a royalty-free licence, to help it compete with VMware's proprietary equivalent. "Microsoft has absolutely got the interoperability message," says Crosby.

3. Xen: Old head on new shoulders
On the face of it, Xen may seem like a newcomer, but the software has been evolving for nearly four years, and has impressed reviewers with its solidity. Moreover, its open source approach (it is licensed under the GPL) has helped it toward broad industry support.

The support of Linux distributors has been key; Xen will be built into versions of Red Hat Enterprise Linux and Suse Linux Enterprise Server arriving this year, among other distributions. With this integration comes automatic certification on all the hardware that those distributions run on, according to Simon Crosby, chief technology officer at XenSource, the commercial company founded by Xen's initial developers. Sun will add Xen support to OpenSolaris this year, and it will arrive for Solaris 10 next year.

The same dynamic has meant that Intel and AMD have both rushed to contribute to the project, meaning it already supports both companies' hardware-based virtualisation, well in advance of Microsoft. (VMware also works closely with Intel and AMD and supports Intel's VT and AMD's SVM.) "Intel has been a major contributor with VT, and that means AMD contributes, because they can't afford not to," says Crosby.

Xen already beats VMware on some basic virtualisation features, for instance supporting up to 64-way SMP, to VMware's 4-way limit, Crosby points out.

Such accomplishments explain why people take Xen's ambitions seriously. "We are surrounding ourselves with an ecosystem of players who are economically motivated to work with us," says Crosby. Xen itself only carries out the virtualisation part of the puzzle, but its universal availability creates a huge, wide-open opportunity for partners to step in with virtualisation-aware products to handle more advanced management and administration tasks, Xen developers argue.

XenSource itself will be just one of these, with products such as Xen Enterprise, a "bare-metal" answer to VMware's ESX Server. In April Virtual Iron launched version 3 of its virtualisation platform, scrapping its own virtualisation engine in favour of Xen.

Crosby argues that Xen's open approach is its main advantage over VMware. VMWare has an incentive to own the market for tools based on its platform, and its control of that platform means it can kill off competitors at will, Crosby says. By contrast, XenSource says it isn't aiming to own the Xen ecosystem.

Analysts agree this is a big selling point. "Some of the big players may be beginning to feel they've ceded too much control to VMware now. They're nervous about it as a control point," says RedMonk analyst James Governor. But whatever its momentum, Xen has so far barely scratched the surface of the marketplace — it didn't even register in a survey of large North-American businesses carried out by Forrester earlier this year. "Certainly Xen is nowhere near as mainstream as VMware yet," says Governor.