Regarding the RAID6 thing -- I have seen plenty of shops that try to run databases on RAID5/6 and yes it isn't pretty, but that's how they do.
This annoys me greatly. There is nothing inherently wrong with RAID5/6 as long as your use is within certain bounds. This sort of thinking gets us stuck with a glorified address book that requires a MySQL Cluster instead of a simple Sqlite DB.
Set your requirements and your budget, and then find a system that works within those two limits.