Like physical disk drives, virtual hard disks can become fragmented. Defragmenting disks rearranges files, programs, and unused space on the virtual disk so that programs run faster and files open more quickly. Defragmenting does not reclaim unused space on a virtual disk.
There must be adequate free working space on the host system to defragment a virtual hard disk. If the disk is contained in a single file, for example, you need free space equal to the size of the disk file. Other virtual hard disk configurations require less free space. You cannot defragment a virtual hard disk while it is mapped or mounted.
To defragment a virtual hard disk for a selected virtual machine, select Hardware tab, select the virtual hard disk, and select Defragment from the Utilities menu., click the