Virtualization can help IT managers allocate more resources with less hardware, but not without introducing a slew of management challenges.

Server virtualization makes it possible to run multiple applications and operating systems on fewer hardware resources, which appeals to many IT managers looking to improve utilization. According to a recent Forrester Research poll, respondents have virtualized about one-quarter of their servers and plan to have close to 50% virtualized in two years. As enterprise IT teams look to broaden their server virtualization deployments, it's important to get in front of the management challenges, according to industry watchers and IT managers.

"Virtualization is a rather addictive technology and IT organizations are spinning out virtual machines faster then they can manage them. The technology warrants a management investment from the start," says Stephen Elliot, a research director with IDC.

For those who are struggling with how to manage virtual machines, here are answers to six important questions.

1. What's so tough about managing virtual servers?

Some will tell you that managing virtual machines varies little from managing physical servers, and others will say it depends on what you're managing. But all agree you need to have a comprehensive management plan in place before widely deploying virtualization in production environments.

"Management is not a single discipline. It can range from business continuity planning to patch management," says Andi Mann, a research director at Enterprise Management Associates (EMA). In the case of business continuity planning, virtual servers could be considered easier to manage than physical servers, Mann explains, but when it comes to patching multiple systems, the virtual world introduces complexities. "You can't always be certain if all virtual systems are patched, and obviously that's a problem," Mann says.

Consistency and standardization also become a bigger issue when managing virtual servers alongside physical machines. The perks of virtualization include easy-to-deploy resources, and that demands IT managers have predefined configuration parameters for application and database servers, for instance. Experts say keeping configurations accurate and up-to-date becomes more critical in the virtual environment because configuration drift is more apt to happen on virtual machines. The same goes for patching.

"The focus shifts to managing templates and preventing drift," says Jasmine Noel, principal analyst with Ptak, Noel and Associates. IT managers would ideally create a standard template that details the operating system, vendor software, patch levels, custom code and more. The template would be maintained so that every new virtual server deployed remained consistent with the predefined standard. Patching would also become part of the template, Noel says.

Beyond maintenance and availability management, another key management issue is performance. The complexity of a virtual environment makes determining the root cause of performance issues a more daunting task, industry watchers say.

"Performance management becomes trickier because for the more difficult problems you'll need to understand how physical server issues manifest in the [virtual machines] and vice versa," Noel says.

While virtualization provides flexible resources, multiple virtual machines residing on one box compete for the same resources and IT managers need to keep that in mind.

"No longer do you have the limitations of just what is in the server shell, but you have to worry about what else is in that box and what it needs," says Edward Christensen, director of technical operations at Cars.com in Chicago.

The online automotive company uses VMware to virtualize servers on HP boxes in its development and quality-assurance environments. "Where you used to think, 'I have a two processor/16GB server,' you are now thinking, 'Do I have two processors and 16GB I can use or is [a particular virtual machine] taking that up or needing it also?'" he adds.