The Burton Group is one of IT's leading analyst firms. They research IT architecture, infrastructure, governance, new technologies and other IT-relevant strategies and create detailed advisory reports. In a recent free report, the Burton Group covered the popular topic of Server Virtualization. In a particular section they covered disk performance and correctly granted that subject significant importance. Here are some quotes from the paper: "Over time, the fragmentation will continually degrade performance of the virtual disk." "File writes and deletions will fragment a virtual hard disk, like any physical hard disk, over time. Running scheduled disk defragmentation operations at periodic intervals or using a disk defragmenter application that defragments disks in real time is the best approach to prevent fragmentation-related disk performance degradation." Of course Diskeeper Corp strongly recommends the real-time approach as the most effective and modern method for solving fragmentation. You can sign up to access Burton Group's free papers including the one mentioned above here.