According to Microsoft, there's more than meets the eye as far as the defragmentation process in Windows Vista goes. Defrag was revamped in Windows Vista, and the overhauling has been met with criticism due to the fact that Microsoft has scrapped the Defragmenter display reducing user control and interference to a minimum, by automating the process.
Victoria House, one of the Microsoft Defrag developers explained Vista's defrag changes on The Filing Cabinet. “One change that’s not obvious to users is our shadow copy optimization during defragmentation. Defrag has special heuristics to move file blocks in a way that will minimize the copy-on-write activity and shadow copy storage area consumption. Without this optimization, the defragmentation process would accelerate the deletion of older shadow copies,