Virtualisation has become one of the hottest topics in IT, although many observers fear that it is becoming too complicated.

As an indication of the growing level of complexity, the Hewlett-Packard Technology Forum that starts Monday in Las Vegas will feature as many as 87 user training sessions on virtualisation, more than any other category..

Despite the appeal of virtualisation as a way to use IT resources more efficiently, the technology adds a layer of complexity that IT managers may not be prepared for and may reduce the anticipated return on investment.

The number of virtualised servers deployed by businesses is exploding "like bacteria in a petri dish," said David Gee, vice president of marketing for HP Software.

Users say they face the same management issues running a virtual environment as a physical one.

"I have to track and monitor who gets access to what; who created it; are they allowed to do this?" Gee said.

Virtualisation can make a single physical server act like multiple logical servers, improving server utilisation. It allows one server to run multiple software applications simultaneously, reducing the number of computers needed. While virtualisation is commonly used in server environments, it's also being used in desktops, storage arrays, networks and for disaster recovery.

But using virtualisation to consolidate the number of physical servers doesn't mean your management duties shrink proportionally.

In March, CA said that 44 percent of 800 IT professionals surveyed globally "were unable to declare their virtualization deployment a success."

That survey showed that 28 percent of respondents failed to see the return on investment (ROI) they anticipated, or couldn't determine if they had. Forty percent didn't achieve the cost savings they expected, or couldn't determine if they had.

For one thing, companies don't necessarily save on IT staff costs by virtualising, said Peter Richardson, director of product management at CA.

If a company that runs 300 operating systems on 300 servers reduces that to running 10 virtual servers on each of 30 physical servers, it still has 300 OSs, and related software applications, to manage, said Richardson. Moreover, as more virtual servers are added, those 30 physical servers could be running as many as 500 applications.

"You could go around universally and ask any client that has virtualised whether they reduced staff and the bottom line is no," he said. Staff isn't reduced because server sprawl continues, even if it's just virtual.

Of course, CA is making the point to promote its own virtualisation management software, which, Richardson says, manages virtual environments even if there are different brands of servers on the network.

Server vendors offer virtualisation management software, such as HP's ProLiant Essentials Virtual Machine Management software. There also are a few good niche management software products available, "but there is still no fully cohesive virtual management suite," said Andi Mann, senior analyst with Enterprise Management Associates.

The HPTF sessions should answer a lot of questions for HP customers about whether virtualisation will live up to its promise, said Scott Healy, chairman of the IT User Group (ITUG), which is co-hosting the HPTF with the user group Encompass. Healy is also a vice president of IT at Sabre Holdings.

"The promise of virtualisation is when you are able to use servers for different applications at different times without impacting the general availability of your IT resources. Balancing that is a concern for any IT manager," said Healy.