I put 4 DD, it is quite easy to use.
I just regret that my VPN connection via a third party server may not be compatible and even on forums not found the solution. I'm not the only one, ca reassuring. This is also the only flaw that I give him. Just a bit noisy if you want to nitpick, as are 4 in DD must not exaggerate either :).
I highly recommend especially for a 4-bay NAS.
Packing and perfect sending speed as usual.