The benefit of virtualizing x86 servers is clear: break the link between software and hardware and create the foundation for a more dynamic, flexible and efficient data centre. With the market for virtualization software expected to grow to more than US$1 billion this year, companies are more than kicking the tires on the technology. But the road to a virtual data centre isn't without its twists and turns. The move to a virtual environment must be done carefully and with an understanding of how the new infrastructure will change IT planning and management. What follows is a list of eight virtualization "gotchas" -- hurdles that users may face as they deploy virtual environments -- that we've compiled through discussions with IT professionals, analysts and vendors.

1. Forgoing the physical: The idea of moving to a virtual environment is to run more virtual workloads on fewer physical systems, but that doesn't mean hardware moves down on the list of priorities. If organizations don't carefully consider what physical resources are necessary to support virtual workloads and monitor the hardware resources accordingly, they may find themselves in trouble. "With virtualization, it's really a matter of putting the right physical systems behind it," says David Payne, CTO at Xcedex, a virtualization consulting firm based in Minneapolis. "Some people think they can buy a cheap system from Dell or HP, throw in the hardware, then put virtualization on top of it and have their virtual environment. But many times that's done based on commodity price, rather than really considering what the virtual workloads are going to be. The companies we've worked with that have been most successful have paid a lot of attention to the planning portion and they end up with a really good result, getting high utilization on these systems and a really good consolidation ratio."

2. Sub-par application performance: While virtualization is becoming increasingly widespread, many applications aren't yet tuned for virtual environments. For example, Daniel Burtenshaw, senior systems engineer at University Health Care in Salt Lake City, deployed VMware's ESX Server about a year ago with mostly good results. "Our biggest issues have been with some of our application vendors not being willing to support their applications on virtual servers, as well as limitations with the version of ESX that we are using," he says. The healthcare organization has a large Citrix environment, but when it moved some of its Citrix servers into the VMware environment, it found that performance didn't keep up, Burtenshaw says. "Basically, we get a very limited number of users per server, so if we virtualize, a bunch of virtual servers on a host is equivalent to just having one physical host," he says, adding that his firm is upgrading to VMware's Virtual Infrastructure 3. "From what we have read -- but we have not tested it yet --Virtual Infrastructure 3 is supposed to be optimized better for hosting Citrix, so we should be able to get a more normal user load on the virtual servers."

3. Sneaky security: Once you deploy a virtual environment, you're removing the link between hardware and software, which can create confusion when it comes to securing your infrastructure. "The decoupling risks blinding security pros to what is going on behind their network security appliances," says Allwyn Sequeira, senior vice president of product operations at patching specialist Blue Lane Technologies. "The server environment gets more fluid, more complex and the security pros ultimately lose the stability that hardware offered. Any type of vulnerability scan could be rendered obsolete in minutes." Dennis Moreau, CTO at security and compliance firm Configuresoft, agrees. Virtualization streamlines provisioning and processes such as patching, but it also adds complications that IT professionals may not be thinking about. "We always had to patch the operating system and the application, and you still have to do that when you virtualize, but now, all of a sudden, you also have to patch the [virtual machine manager] layer where vulnerabilities can exist," he says. "So the work of maintaining a secure environment and of documenting that for compliance purposes, just by the fact of introducing a virtualization technology layer, gets more complex."

4. Left in lock-in: The virtualization market is evolving quickly and even VMware is pushing for a standard way to create and manage virtual machines. But standards and interoperability will come slowly. Companies that aren't careful may find themselves locked in to a certain vendor's approach, making it difficult and expensive to move among other approaches as technologies mature. "Try to pick products that can be considered somewhat standard and open to the virtualization market, like products where you can import [virtual machines] from other products," says Ulrich Seif, CTO at California-based National Semiconductor. "Too many things can happen in this space in the next couple of years, so don't corner yourself if you can help it."