HP IBM Sun VMware

Server virtualization is an action item on nearly every IT agenda these days. Gartner predicts that by the end of next year, 25% of the Fortune 1000 will use partitioning - a key virtualization technology - for their Windows server deployments. And by 2008, the firm estimates, companies that don't leverage virtualization technologies will spend 25% more for their Intel servers and 15% more for RISC servers, including hardware, software, labor and space.

Still, users might have a hard time drawing a bead on the various server virtualization architectures - what the strategies are, which are best for their environment, which will accommodate virtualization needs for storage and network resources, and how much the architectures lock them into the vendors' products.

Part of the problem is, server virtualization is a moving target. "A lot of things are considered virtualization," including partitioning, workload management, server provisioning and server automation, says Jamie Gruener, a senior analyst at The Yankee Group. "If there's a nail, virtualization is [the vendors'] hammer."

Most IT experts agree on the definition of server virtualization, but vendors offer varying ways of achieving that goal. "The idea is to present the illusion of one huge machine that's infinitely powerful, reliable, robust and manageable - whether it's one machine that looks like many, or multiple machines tied together to look like a single system," says Daniel Kusnetzky, a vice president with IDC.

The best users can do is ask questions (see "What to ask"). "They have to take a look at what servers are in their environment, how they manage them as a group, what they could do to reduce their amount of management time and ask vendors how they can use their platform in a heterogeneous fashion," Gruener says.

Laying the groundwork for those questions, Network World recently spoke with the top server vendors, and VMware (an EMC company) with its pervasive solution for x86-based machines, about their virtualization architectures. Here's a look at how HP, IBM, Sun and EMC/VMware define virtualization and at how their products fulfill that definition.