Hey Rototype,
This discussion never ends and have been talked about in many thread... No need to bring back a 5 years old thread about that...
About consumer grade HDD, just don't do it. Their firmware has not been programmed for NAS. Here is an example :
One hard drive has a hard time reading back a sector. What will it do ?
The NAS hard drive was programmed for operating with other drives in a redundant structure. So for that one, it does not matter not to be able to read THAT data. Other drives will do it. So after a few tries, it will return an error saying "Sorry, can not read that one!". The NAS will turn to the other drives right away, recover the data, serve the client and then go on to fix the unreadable data on the problematic drive.
The other drive is your regular desktop drive. That one considers it is the only one holding that data. So no matter what, it MUST read it back because if not, the data is lost. So the hard drive will fight over again and again, sometimes for minutes before either reading back the data or giving up. Poor performance, poor management of drive space and more problems with that one.
These desktop drives are not meant to run 24/7, to sustain that heat, that much vibration and more.
You are million time better with actual NAS drives.