Upload & Sell: On
Consider a ZFS server. I built an 8 drives server. Cost me a little more than a 8 bay Drobo, but have better redundancy, and more space (8x2TB gives me 10TB of usable space).
Check it out:
It's also more efficient and faster than any hardware based RAID arrays
OpenSolaris can be a PITA. I went with FreeNas based ZFS system. Not quite as fast, but a ton easier to get up and running.
To the OP, what are you planning on using this for? A NAS may not be the best choice.