You can use nodupes like fdupes or mp3dupes, to scan your hard drives looking for duplicate files.
$ nodupes directory
To add a media :
$ nodupes --add-media name_of_media directory_of_media
To remove a media :
$ nodupes --remove-media name_of_media
To list existing media :
$ nodupes --list-media name_of_media directory_of_media