Using Python 3.5+ os.scandir() optimized variant.
Starting.
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*Collecting tree differences
Skipping system cruft (metadata) files in both FROM and TO
comparing [/MY-STUFF] [/Volumes/SSDT3/MY-STUFF]
excluding /MY-STUFF/__bkp__
excluding /Volumes/SSDT3/MY-STUFF/__bkp__
comparing [/MY-STUFF/__more__] [/Volumes/SSDT3/MY-STUFF/__more__]
...
------------------------------------------------------------------------------- 
*Summary
Compared    => files: 59521, folders: 3967
Differences => samefile: 215, uniqueto: 38, uniquefrom: 87, mixedmode: 0
Changed:
files   => created: 0, deleted: 0, replaced: 0
folders => created: 0, deleted: 0, replaced: 0
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Finished.