A simple way to back up your data from one drive to another is rsync. The magical incantation (assuming the data drive is /dev/sda1 mounted on /data and the backup drive is /dev/sdb1 mounted on /databackup, and you normally keep the backup drive mounted read-only):
sudo mount -o remount,rw /dev/sdb1 /databackup
sudo rsync -a --delete --progress /data/ /databackup
sudo mount -o remount,ro /dev/sdb /databackup