Throughout the years, there will be more and more files stored on a NAS. In emergency cases, a 'backup' has to happen as quick as possible, so files are simply copied into a target folder outside of regular backup strategies.
There is a linux tool called 'fdupes' available, which can help to identify duplicates or empty folders or broken symlinks and so on. On a huge data set, the runtime is very long. This container image wrapping this 'fdupes'-command might help, so that the processing can be moved on a NAS (or similar) server.