Commonly-used command lines for my home backups:
ssync --update-only --no-sync-meta --no-detach --src-path /Volumes/homes/mail/ --dst-path /Volumes/Hotwired/Backups/Mail/
or:
rsync -rv --size-only /Volumes/homes/mail/ /Volumes/Hotwired/Backups/Mail/
rsync -rv --size-only /Volumes/disk\ 1/Pictures/Photos/ /Volumes/Hotwired/Backups/Pictures/Photos/
(see also cdrecord and hdiutil for a couple of incantations to burn the resulting filesystem)