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 aes128-gcm@openssh.com -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.