It's not the cheapest solution, but I have a Drobo for back up and it let's me sleep at night. After having many a back-up external drive fail, I settled on the Drobo, and it blows away the RAID array it replaced as far as ease of use.
I looked at this. It does look impressive but I worry that the Drobo itself becomes the weak link in the chain. Currently, I am considering a NAS LaCie 2big with two 1 TB dives that run mirrored on RAID 1. I figure even if the LaCie dies I'll still easily have access to the data either of the two mirrored drives.
Is my logic correct ? I am not sure. I was certainly tempted by the Drobo and all the hype it is getting in magazines.