"Doing P-to-Vs, or physical to virtual conversions, there's a black art to it if you will," Pradel says. The conversions "don't happen in a vacuum. That happens in conjunction with different business units' schedules and the ability to withstand downtime."
3. Virtualization automatically reduces power use
If you have consolidated onto fewer servers, it might be tempting to say "I've solved my power use problems." Not so fast. While you now have fewer servers using up watts, each server is running at a higher CPU capacity and has greater power needs. At Brandeis University in Massachusetts, a virtualization project has actually increased overall power use, reports network and systems director John Turner. Although Brandeis dramatically reduced its number of servers, it is now offering more services to users because spinning up new VMs is so easy. Each new workload increases power use.
"If you walk behind the racks of virtualized servers, the heat is just pouring out of those guys," Turner says. "We're seeing heat dump into these rooms like never before."
Another issue to consider: If you're shutting off lots of servers, a data center has to be reconfigured to prevent cooling from being directed to empty space, explains APC CTO Jim Simonelli.
"The need to consider power and cooling alongside virtualization is becoming more and more important," he says. "If you just virtualize, but don't alter your infrastructure, you tend to be less efficient than you could be."
4. Virtualization makes me safer
The ability to clone VMs and move them from one physical box to another opens up great possibilities for disaster recovery -- and that in turn protects your business from data loss and downtime. But virtualization, if not managed properly, also brings new security risks that could threaten the safety of data and continuity of business systems.
People and processes are often not ready for virtualization and the security risks it introduces, IBM security expert Joshua Corman has argued.
Virtualization brings new attack surfaces and various operational and availability risks. Consolidating many applications onto a single server "gives you a single point of failure," DiDio notes.
If you're suffering from virtual server sprawl, it may be difficult to keep track of all your VMs, and it may thus be difficult to ensure that all of them are properly patched. Also, hypervisors do not perform encryption, leaving open the possibility of man-in-the-middle attacks such as Xensploit, which intercepts unencrypted data when VMs are migrated between physical servers.
That doesn't mean you should avoid virtualization altogether, but it's often best to start with minor systems and work your way up to mission-critical applications.
5. Desktop virtualization will save me money right away
Sign up for Computerworld eNewsletters.