The only thing that's automatically duplicated is the CoveFS metadata on the pool (the hidden .covefs folder).
While not an auditing tool, you can use the folder duplication window to see if a folder contains duplicated files. It actively measures each folder as you selected it, and thus will show you with byte by byte accuracy what exactly is duplicated and where (albeit on a folder level).
The .covefs folder is hidden in that window, and I kind of went back and forth on whether we should show it or not. I think maybe we should, and simply call it [METADATA] or something similar.
Let me make that change.