The problem may not rival the movies "Poltergeist" or "The Amityville Horror" for sheer terror, but CIOs and datacenter managers are still well advised to deal decisively with so-called ghost servers. Like celluloid zombies, these forgotten pieces of equipment are dead when it comes to improving the bottom line, but they are very much alive when it comes to eating up IT budgets.

The unproductive -- and usually undocumented -- servers take up valuable real estate, consume increasingly expensive electricity, and in some cases, absorb ongoing maintenance and lease payments.

"You can find ghost servers in a lot of enterprises," says John Phelps, an analyst at Gartner. "And the larger and more diverse the company, the harder it can be to have a single group or technology platform that provides control over all corporate assets."

Sun Microsystems, through case studies of two large corporate datacenter operations and anecdotal analysis of efforts with many customers, believes that 8 to 10 percent of all servers in large corporations have no identifiable function. In the two datacenter studies, 150 ghost servers were found in an installation of 1,800 servers, and 354 ghost servers were found in an installation of 3,500 servers.

One of the companies studied was Sun itself. Sun used system performance tools to monitor CPU utilization and I/O and network traffic, collecting the data over the course of a month, and sorted out machines with zero utilization.

Sun removed the questionable servers from operation for 90 days to determine any impact. At the end of the period, it found that 60 percent of the servers could be permanently decommissioned, says Mark Monroe, director of sustainable computing at Sun. The company now conducts quarterly reviews of utilization rates.

"It's hard to get people to admit they have unused infrastructure," Monroe says. "It's expensive, wasteful, and having a CIO admit he's got millions of dollars of idle assets lying around could get a guy fired. I think we can remove some of the stigma by talking about the facts, and having people realize it's worse just to leave them lying around."

Corporations need to admit "they are like everyone else" and try to reduce the number of idle machines to 3 percent or less, "which is three times better than the industry average," he says. The cost of running a server for three years exceeds its original acquisition cost, so keeping the ghost servers around has an easily measured effect in energy savings. Identifying and eliminating wasted resources are key components of green or "eco-computing," Monroe says.

The good news: Advances in asset management and configuration software can help businesses find and shut down these useless machines. And more companies are being proactive when it comes to adopting policies in this area. A survey of more than 300 businesses in the United States and Europe conducted by Gartner in 2006 found that 74 percent of respondents said they have a formal software and hardware asset management program.

More advanced autodiscovery capabilities and more efficient, effective, and accurate search engines mean "there has recently been more focus on discovering the lost and unidentified equipment, especially in industries where security concerns are growing," says Richard Ptak, analyst at Ptak, Noel & Associates. "Every major company I've ever dealt with has had the problem to some level."

When BlueCross BlueShield of Florida (BCBSF), which provides insurance services for nearly 9 million people, decided to build a new datacenter in 2005, the company also felt it was time to get a comprehensive look at its asset inventory, says Paul Stallings, senior manager for provisioning services. In addition to the new and existing datacenters, BCBSF also has about 10 smaller server rooms in various locations around the state.

The server room equipment was being managed by different departments within the insurance provider, and each had a different way of tracking and documenting assets, Stallings says. Using Aperture Technologies' VISTA tool beginning in late 2005, BCBSF began documenting its IT resources under a single umbrella.