I have 8 harddisks on my system,
Defragging them can really be painful, too long to wait.
I found the way that defragmentation speed can be boosted up.
for example i have disk C as system and D,E,F for data
i need to defrag disk E
defraggler can check for available space on disks D & F
and made moove operations from disk E to D and back from D to E
it can be faster with long (more than 2Gb) files.