I want to upgrade my NAS (Synology DS409+ with 4x 2TB drives) because I need more capacity and this article has made me think of building my own WHS server. One question though, my current NAS runs in RAID5 mode and with 4x 2TB drives I have about 6TB capacity and protection from a single drive fail...

I fitted two120mm Nexus Real Silent Case Fans (1000rpm), one intake at the front and one exhaust at the back. I removed the top fan blocked the top opening.
These Nexus fans are super quiet and above all very inexpensive!