I think you're right ... Though that rsync paper was really cool to read through In our case, the files are rarely being _modified_, rather they're mostly being added or removed. So we really only need the full-file checksum that we do now. The difference in our case that makes things tricky though is that we lose filename + directory structure on the Empeg side, so we have to _find_ the files on the PC side. One way around this is to keep an index file of computed hash codes at import time, but that's really just as bad as storing the source filename in a tag, since if the file moves or changes name, they'll no longer be in sync. It's just a tricky problem in general.