Need Help--to get the right external hard drive to expand, backup & use raid for security

Using Windows Vista Ultimate on a Gateway P6860fx & want to expand and backup using an external hard drive. 

My pc has 1 esata port. Looking at the Sentinel DX4000 with 8tb. Just using my pc at home for personal use though. My existing system needs room so my pictures will be moving first. Have not made any purchases yet.

Suggestions are much appreciated.

The Sentinel sound like overkill for home use. I would go with the My Book Live Duo 8TB of the My Book Thunderbolt Duo 6TB if you need a faster connection.