Everyone knows that server virtualization shaves hardware clutter in the datacenter, boosts workloads, brings disaster recovery flexibility, slashes costs and basically saves the planet from nasty carbon emissions. But here's the dirty little secret: Many pitfalls await server virtualization adopters, and a stumble can ruin all your virtual dreams.

The sheer number of potential missteps has Doug Dineley, executive editor of the Test Center, shaking his head. "Virtualization offers irresistible benefits, and also the opportunity to drown."

It can be shocking to suddenly realize that your IT staff is woefully unprepared for virtualization and needs training. Or maybe you'll stumble out of the gate, not knowing that it takes at least a month to get a grip on your server environment. You might be pressed to free up money to cover hidden costs or purchase new equipment -- yes, new servers will likely be needed for what's supposed to be a server consolidation project. Even if you navigate these and other pitfalls, you'll likely be blindsided by virtualization vendors' over-the-top performance claims.

What's behind the virtualization buzz

Server virtualization breaks up the marriage of hardware and software (in this case, between the physical system and operating system software), and thus allows a single physical server to host many virtual servers running different operating systems. The benefits of this basic capability border on computing nirvana, not the least of which is server consolidation. For instance, IBM started moving the workload of its 3,900 servers to 30 virtualized System z9 mainframes running Linux. Big Blue expects to cut energy consumption by 80 per cent, or more than US$2 million in energy costs. Meanwhile, NetApp consolidated 343 servers to 177 via virtualization and replaced 50 storage systems with 10 new ones.

Indeed, the front lines are awash with server virtualization success stories -- and the drumbeat grows louder every day. EMC's virtualization high-flyer unit, VMware, raised nearly $1 billion in its public offering last summer, based on a highly regarded product. Citrix Systems, which acquired server virtualization vendor XenSource in December, took the wrappings off of XenServer 4.1 earlier this month. Last week, market researcher Gartner called virtualization "the most important trend for servers through 2012."

Now Microsoft plans to shake up the virtual world with its Hyper-V, a virtual machine manager, or "hypervisor," the company is building into Windows Server 2008. Currently in beta and due out this summer, Hyper-V has already stirred debate among Test Center reviewers. Chief Technologist Tom Yager applauded the offering in February, while Paul Venezia panned Hyper-V in a Test Center preview two months earlier, citing, among other things, that his attempts to run the disk manager often resulted in a lockup. "It has a long way to go to be production-ready," Venezia wrote.

Further, Hyper-V will come to market lacking advanced features, such as live VM migration, that have long been present in VMware's enterprise offering. On the other hand, Hyper-V comes "free" as part of the operating system; and Microsoft's integration of virtual machine management into its pantheon of management tools is sure to be a hit with Windows shops.

Marketing buzz aside, the truth is that server virtualization fundamentally changes the way a datacenter looks and feels -- and no major transformation comes easy.