Hi,
I've seen something which can be normal but not very clear in documentation :
http://www.piriform.com/docs/defraggler/advanced-usage/command-line-parameters
df.exe C:
or
df.exe C:\
Don't to the same thing.
The first one defragment the entiere drive.
The seconde one, only the root drive without subfolders.
I think, a little precision could be useful
++
Vincent