You will need to add the volume to your /etc/fstab. Make a backup of it first "cp -p /etc/fstab /etc/fstab.bak", then edit it and view the line for your volume that is already auto-mounted. You will need to add a line for your second volume and it will mount on boot.
Check out the steps on towards the bottom of the page on manually adding it to /etc/fstab. Why let a tool do it for you when you could learn how and why it works easily enough?