Perform free-space consolidation. Free-space consolidation is useful if you need to shrink a volume, and it can reduce fragmentation of future files.

Track an operation already in progress on the specified volume.

Run the operation at normal priority instead of the default low priority. Specify this option if a computer is not otherwise in use.

Defragment multiple volumes simultaneously, in parallel. This is primarily useful for computers that can access multiple disks simultaneously, such as those using SCSI- or SATA-based disks rather than disks with an IDE interface. 

Defrag from the Command-Line for More Complete Control