 physical server. Virtualized servers enable multiple operating systems as well as multiple applications to reside on the same server. Large cloud providers commonly have multiple data centers that contain replicated copies of all data. If a data center becomes disabled, another can easily take over its functions. Virtualization makes it less costly and complex for providers to support multiple data centers in different physical locations. This results in a reduction of physical services, less electrical power, and less cooling, thus lowering providers' energy costs. Moreover, virtualization enables data centers to support multiple developers by providing a virtual computing platform for each developer while he is logged on to a virtual machine. Multi-core processors enable multiple developers to simultaneously log on to the same physical server. When a developer logs off from his area of the server, computing power is freed up for other uses. Because of security and privacy concerns, large companies often do not want their applications and files on the same physical servers as those of other organizations. In these instances, they can elect to www.TechnicalPDF.com reserve a group of servers for their own use. Amazon refers to this feature as a Virtual Private Cloud. Other providers offer similar features. Not surprisingly, there is an extra monthly fee associated with this service. MANAGING VIRTUALIZATION Organizations can realize many benefits by implementing virtualization capability in servers and storage networks. They also take on challenges managing them in complex environments. Managing Memory, Virtual Machines, and Disk Storage in Virtualized Data Centers Server virtualization has many benefits, including saving money on electricity, heating, and cooling. However, there are challenges in large data centers. One such challenge is managing memory in the host physical servers. Newer operating systems installed on host servers have more code and require more memory to operate. IT staff members allocate memor