I've gone back and forth on whether I need RAID locally. Giving up at least a third of your storage capacity (assuming RAID 5) for the off-chance that your hard drive dies in 3-4 years seems like a high price to pay. I had two drives fail in the lifespan of my current desktop. And I had enough warning from SMART that I could peel off the data before the drives bricked. I know I got lucky, but still...