Now that`s a fan.
But, not really where it will do the most good for a NAS application. The hard drives are mounted in the lower front part of the case. While that fan will help to introduce cooler air into the case it will primarily only help cool the mobo = chip set, processor, and video card before being drawn out the back.
IMO, the main heat concern for your application need`s to have air moving front to back. I can see in the pictures that the there is a place in the rear of the case to add what looks like a 120mm fan. Can`t tell if the case will accept a fan in the lower front or not.
These would be the two areas of biggest concern in my mind.
Hard drives do produce heat. That case has 6 3.5" bays, where the drives will mount. There is little or no room between them for air flow. 5.5" to 3.5" adapters can be bought which will allow the drives to be mounted where optical drives would normally go. That will allow better spacing between them for better cooling.