n virtualized servers, the number of applications can escalate rapidly. Data centers that previously had 1,000 servers with a 1,000 applications can potentially now have eight images per physical server and 8,000 applications to manage. Another cause of server sprawl occurs when an application is upgraded. To test the application before it's upgraded, management creates an image of the application, upgrades the image, and then tests the upgrade on a small group of users before making the upgrade avail- able to all users. However, often the original and the upgraded application are left on the physical server, which further contributes to sprawl. To complicate matters further, if either the original or the upgraded version is moved to a different physical server, it can be difficult to determine that there is a duplicate. Managing Virtualization Software to Monitor Virtualized Data Centers Small data centers with only one or two physical computers holding virtual computers are generally easier to manage than the same data centers with perhaps 20 applica- tions installed on 20 physical servers. However, there is a learning curve for managing numerous physical servers, each running multiple operating systems and applications on virtual computers. It involves keeping track of which physical server each image resides on as well as the application's address. For large data centers, it is often easier to manage physical servers, where each one can be physically observed, than to man- age an array of applications on virtual computers. To do this properly, a good suite of management tools is required. Moreover, because problems can occur in switches, servers, and storage, the best management suites are those that are capable of diagnosing and monitoring all of these areas. Vis- ibility across these three sectors is complicated by the fact that in many data centers, different manufacturers supply the switches, servers, and storage. One solution is use third-party suites of management software that are capable of monitoring