jdupes, rdfind, fclones and possibly many others compute checksums of prefixes (and sometimes suffixes) of the files. That reduces the number of files to be ful

jdupes, rdfind, fclones and possibly many others compute checksums of prefixes (and sometimes suffixes) of the files. That reduces the number of files to be fully hashed. Computing incremental checksums in parallel and breaking up once checksums diverge does not work very well on HDDs because the files can be in distant physical locations, and that would cause lot of seeks (seeks are terribly slow on rotational drives).