Each method of virtualization has its advantages, depending on the situation. A group of servers all based on the same operating platform would be a good candidate for consolidation via OS-level virtualization, but the other technologies have benefits as well.

Para-virtualization represents the best of both worlds, especially when deployed in conjunction with virtualization-aware processors. It offers good performance coupled with the capability of running a heterogeneous mix of guest operating systems.

Full virtualization takes the greatest performance hit of the three methods, but it offers the advantage of completely isolating the guest OSes from each other and from the host OS. It is a good candidate for software quality assurance and testing, in addition to supporting the widest possible variety of guest OSes.

Full virtualization solutions offer other unique capabilities. For example, they can take "snapshots" of virtual servers to preserve their state and aid disaster recovery. These virtual server images can be used to provision new server instances quickly, and a growing number of software companies have even begun to offer evaluation versions of their products as downloadable, prepackaged virtual server images.

It's important to remember that virtual servers require ongoing support and maintenance, just like physical ones. The increasing popularity of server virtualization has fostered a burgeoning market of third-party tools ranging from physical-to-virtual migration utilities to virtualization-oriented versions of major systems management consoles, all aimed at easing the transition from a traditional IT environment to an efficient, cost-effective virtualized one.