By now, almost everybody agrees the buzz about server virtualization is justified. It's impossible to argue with the evidence presented by early adopters: This New Data Center technology has indeed let them decrease the number of physical servers they run and increase the number of applications they support -- all while boosting performance and availability, and even easing the overall administrative workload.

These results have not come without trial and error, however. Roughing it out through server virtualization's early years, the pioneers learned a few things that make the technology even easier to deploy and manage. Without a doubt, they say, these five tips will help today's users get the most out of their virtualized server environment.

1. Don't skimp on the hardware.

Although most server virtualization software can run on just about anything and still work, users need to invest in good hardware if they're serious about virtualization, early users say. This is especially important if they're planning to deploy high-transaction database applications or other I/O-intensive apps, they add.

For example, investing in Sun's two-processor, dual-core SunFire 4100 and 4200 servers let Atlanta's energy consultancy NewEnergy Associates fold 20 virtual servers into just one machine -- far more than the seven to 10 applications it had expected to consolidate, says Neal Tisdale, vice president of software development. "The Sun servers have really good addressing speeds with the Opteron processors, and the address bus is four to eight times faster than some of the Intel motherboards," he says. "So the amount of servers we've been able to virtualize is very high."

Similarly, Jason Powell, technology director at Granger Community Church in Indiana, is consolidating 11 servers down to four midlevel Dell PowerEdge servers. Each server, he estimates, costs US$10,000 for the hardware alone but can accommodate as many as six virtual servers easily. This leaves him two extra servers for truly robust failover. "The hardware investment is worth it, because it can really be leveraged, and you end up saving in the long run," he says.

But perhaps the best example is Baldor Electric, a manufacturer of industrial electric equipment. Mark Shackelford, IS director, says he consolidated 45 Linux-based SAP application servers down to just one box, an IBM zSeries mainframe. It runs all the company's mission-critical applications and handles I/O-intensive SAP database applications, he says. "The IBM zSeries is very expensive upfront, but I have a very limited staff," he says. "In the long haul, we've proven that the total cost of ownership of the zSeries is the cheapest there is, especially compared to Intel boxes and their downtime, performance and management costs." (For more on measuring the savings possible with virtualization, see story at right.)

2. Don't virtualize everything.

Baptist Healthcare System has consolidated nearly 200 servers into 15 Intel-based boxes, but that doesn't mean it virtualizes everything, says Tom Taylor, a client/server infrastructure analyst for the healthcare group. "We use [VMware's] ESX Version 2.5, so anything that needs over 3GB of space, requires more than two processors and requires its own USB device or ancillary components like that, we don't virtualize," he says, noting key limitations of the VMware software.

Similarly, applications like Microsoft Exchange are too I/O-intensive to virtualize. "I wouldn't put my Exchange server in a virtualized environment, just because of the high database I/O. It wouldn't be conducive to the platform or technology currently," says Kevin Westman, network systems manager at the University of Chicago, which manages Argonne National Laboratory. An early VMware user, Westman now favors XenSource's open source Xen platform. With it he has consolidated as many as 15 Windows and Linux servers into an Intel-based box.

Baldor's Shackelford agrees, noting Exchange is one of the few applications his firm runs on a dedicated Windows server. "Exchange wants to control the whole box," he says.