rsync --verbose --compress --recursive --perms username@hostname:/from/dir/ /to/dir
rsync -Pav -e "ssh -i $HOME/.ssh/somekey" username@hostname:/from/dir/ /to/dir/

# -e : ssh command e.g. -e "ssh -i $HOME/.ssh/somkey"
# -z : compress
# -v : verbose
# -h : human-readable numbers
# -r : recursive
# -P, --progress : show progress
# -a, --archive : archive mode; equals -rlptgoD (no -H,-A,-X)