There are several switches that may apply but I can't say for sure because I don't have the exact details of your requirements. For example:
/purge deletes files that are no longer in the source
/mir mirrors a directory tree
/mon monitors the source and runs again when changes are detected
If only 80GB then the likely best option is to delete or rename the old destination folder, then copy source to destination again. This will ensure a fresh copy and you can run one of the options above like /mon or /mir to keep the files fresh in both locations.