There's defragging a hard drive, and then there's defraggling it:

Step 4: Remove the disks

When the discs have finally come lööse, keep them in order and don't mixem up If you have Windows on your Data machine, You'll find the OS on the top disc, you'll recognize it easily, it's much heavier then the rest of the discs. If you use Linux, then you'll of course don't need to do this operation at all...

Well, I can say one thing, after performing this procedure you will definitely not have trouble with fragmentation on your hard drive.

Via Jimspot.