Although I would not buy an F4 drive for use in an unraid array right now, if I had one, I may consider using it. How much would it cost to return it? What kind of a deal did you get on it? Can you wait for a deal on something else? If you decide to keep it, I would not use it as a parity drive. I would only use it as a media drive, install it in your array, fill it up, and leave it alone. In that scenario it would be fine. I have three F3 drives and the temperatures they report are in line with the others in the array. I don't see that as reason alone to reject a drive. Reliability, low power and ease of warranty replacement are what I seek.