This is a very good article that explains why RAID arrays are about to become obsolete. I might have liked a few graphs that project when an EMC CX4 would no longer be a viable Enterprise storage option, but overall this article is a gem. If you work in data management, now is the time to start worrying.
The bottom line is this: Disk density has increased far more than performance and hard error rates haven’t changed much, creating much greater RAID rebuild times and a much higher risk of data loss. In short, it’s a scenario that will eventually require a solution, if not a whole new way of storing and protecting data.