Yes that's correct. This is a production system and some form of redundancy is required.

I was just wondering if instead of the layout I suggested, would it be better to just have one array of 10 disks in RAID5 i.e. 9 available disks, capacity=2.7TB and just have everything on the one volume (or split it via Windows into logical drives) - is the advantage of more spindles better than separating database & logs & backups into their own arrays?