Virtual unrealities exposed

Over the past 18 months, the buzz around server virtualisation has gradually evolved to a point where customer demand almost matches the hype from vendors. Yet the technology really is nothing new, as anyone familiar with Unix and mainframes will point out — mainframes were running virtual partitions in the 1970s. So, where exactly is all the momentum coming from?

Virtualisation is a broad term, taking in the virtualisation of input/output (I/O), storage and much else, but the recent interest has been focused on virtualisation of servers — essentially the ability to run more than one operating system on a single piece of hardware. While the technology for this is essentially old hat, it is relatively new to the x86 platform, with VMware — currently dominant in x86 virtualisation — getting into the game in 1998.

It's only over the past few months, however, that virtualisation has really taken off on the x86 world, due to a few different factors — server replacement cycles coming around, more mature management tools for virtualised servers, support for a host of new features such as symmetric multiprocessing (SMP), where two or more processors are connected to a single memory, and growing awareness of how well virtualisation works.

One result is that VMware (owned by EMC since the end of 2003) recently broke the symbolic barrier of $100m in revenues per quarter, a figure that has been doubling year-on-year. In February a Forrester survey of 1,221 North-American companies with more than 1,000 employees found that 41 percent were already using virtualisation or were planning pilot tests; overall, 60 percent said they would spend money on virtualisation over the next 12 months. Forty-three percent said they considered VMware most often for x86 server virtualisation, compared with 24 percent for Windows Virtual Server.

Find out more about the main companies providing virtualisation technology

VMware is unlikely to monopolise this cash cow for long, however, with Microsoft and others keen to push their alternatives. Microsoft's Virtual Server is probably the least mature of the lot, but it is improving rapidly, and the software giant is typically giving the technology away. Moreover, virtualisation will be built into Longhorn Server within months of the operating system's release.

The other potentially disruptive development is the emergence of an open source virtualisation project that seems to have nearly everyone rallying behind it. Xen, which uses a different underlying approach from Microsoft and VMware, is built into the latest Linux distributions from Red Hat, Novell and others, and is getting Solaris support within months.

A more flexible approach
Virtualisation is essentially about abstracting resources such as computing power, storage or applications, creating flexibility in the way the resources are used. VMware was the virtualisation pioneer in the x86 realm, and is largely responsible for its current popularity on x86 servers, a fact even competitors readily admit. "VMware discovered the server virtualisation market. They educated that market for everybody," says Simon Crosby, chief technology officer of XenSource, the commercial software company founded by Xen's creators.

In the operating system virtualisation realm there are several different approaches, which can be categorised by the degree of virtualisation they offer. Software such as the PowerPC version of Virtual PC, for example, emulates the hardware platform completely in software, letting you run an operating system designed for…