With XenSource's recent launch of virtualisation manager XenOptimizer, it would appear that there's finally an open source rival for VMware, which remains by far and away the market leader in the virtualisation space. Can XenSource rev its code in time to catch VMware, which is galloping hard towards the horizon?

Tough call. The obvious answer is "not for quite a while", so big a lead has VMware got -- it's a question we explored last October and little has changed since.

According to IDC, VMware's server virtualisation software revenues have experienced 131 per cent growth between 2003-4, and it has revenues approaching $180 million. The nearest competitor is IBM with $100 million but which is growing at a mere 7.4 per cent.

There appears to be little to slow the market leader. Most observers agree that the company has -- in that hideous phrase -- got its ducks in a row. The product offering is right: it runs on all platforms you'd want, it offers three product layers, Workstation, GSX Server and ESX Server's hypervisor-based consolidation features for the data centre, and it supports the virtualisation technology in forthcoming generations of processor.

What's more, the management tools are there to enable large-scale applications of virtual technology. And VMware has also garnered a wide range of support for its products from third parties, raising the barriers to entry for newcomers -- a standard manoeuvre for established market players.

In terms of the opposition, there's little likely to unseat VMware. Parallels is the latest addition to the virtualisation market. It's a privately held, US-based software company that's just launched its first virtualisation tool, Parallels Workstation, and plans to produce a server version by the start of next year. However it competes only with VMware's Workstation product thus far and cannot present a mature challenge to the leader in the near future.

On the Itanium platform, SWSoft is claiming the market for itself but it's a low volume business and seems destined to remain a tributary for the foreseeable future. However, its Virtuozzo 3.5 for Windows product adds support for AMD and Intel's 64-bit EM64T and AMD64 architectures, something already supported in the Linux version. However, in this area, it's an also-ran.

Meanwhile Microsoft's Virtual Server is currently a Windows-only product -- though this will change in the next version. Virtual Server 2005 R2 has gone to manufacturing and will be released in December. The product will now officially support Linux, and will clearly be a big competitor. What's more, Microsoft's server virtualisation revenues are growing at 32 per cent annually.

However, XenSource's new product will be viewed differently. There's a huge head of steam behind the open source movement, with most Web servers using open source software (OSS). Analysts and market stats suggest that OSS is moving into the mission-critical areas of enterprises too. But the only OSS virtualisation product, Xen, has not made big headway into the virtualisation market.

Xen is been hard to use and install -- they're complex tasks for the unfamiliar because of the product's para-virtualisation techniques, which modify the OS. This has restricted its use to those who can spare the time -- and IT managers are notoriously short of that expensive commodity.

"Xen the open source product is a pretty raw technology. . . . Until now, the majority of deployments have been by people who are Linux experts and have developed their own solutions to roll it out," says XenSource CTO Simon Crosby. "What [XenOptimizer] provides is all the wrapping around Xen that one would need to actually go off and deploy in a normal enterprise environment."

XenSource now says that XenOptimizer fixes that problem and automates the transformation from physical to virtual servers on Linux, providing a dashboard for monitoring control of computing resources, and allowing drag-and-drop provisioning of virtual machines.

As Charles King, principal analyst at Pund-IT Research says: "Xen's market is a good one for them to be aimed at, but there is a huge gorilla [in VMware] they're competing with that is gaining weight fast. They [XenSource] claim to be offering a real significant price/performance benefit, which could increase the uptake of Linux servers."

However, no matter how good the technology, it still takes time to learn and to deploy. While XenSource offers something that the others don't, it'll have to work hard to break the VMware stranglehold.

But at least XenOptimizer provides the lever to do just that. We've an interesting couple of years ahead.