Passwordless SSH access

Generate new SSH keys

ssh-keygen -t rsa -C pi@rapsberrypi

Copy publilc key to destination server

cat ~/.ssh/id_rsa.pub | ssh root@192.168.1.100 'cat >> .ssh/authorized_keys'

Backup script

rsync -avr /home/pi/* root@192.168.1.100:/volume1/Data/rpi_1

Read the full article here on Raspberry Pi homepage.