I sync my MP3 library to a SD card. While a normal
rsync -av takes ages to do that, here is the command I came up with.
rsync -rv --size-only --numeric-ids --progress --delete -e 'ssh -T -c firstname.lastname@example.org -o Compression=no -x' remote-server:/Music/ Music/
Of course, the SSH stuff is optional. But checking by
size-only is sufficiant in my case, because I delete all non-matching files anyways.