Ganz wichtig, und eigentlich ganz einfach, aber ich mache es immer falsch:

SOURCE Source is the directory that is backed up. At least one source is required. A trailing slash on a source path means „copy the contents of this directory“. Without a trailing slash it means „copy the directory“.

DESTINATION Destination is the directory that source is copied to. Trailing slash on the destination directory doesn’t matter.

Quelle: ‎rsync_tutorial‎.md