Non DFS Used?

[David J. O'Dell]

We have a new cluster running 0.20.1 that I just started loading and I 
noticed that my non DFS used is higher than DFS used.
Configured Capacity : 110.08 TB
DFS Used : 4.28 TB
Non DFS Used : 5.58 TB
It can't be any files left over from mapred jobs because I've only been 
running a few for testing.
What comprises non dfs used and how to I manage it?