AnandTech has a good writeup taking a look at the 6 TeraByte version of Western Digital RedPro Drives. These are the 7200 rpm versions of their Red NAS line designed to be in racks with up to 16 drives with firmware tuned for NAS applications.
I’ve been using some of the 3TB non-Pro versions in my Drobo 5N for some time now with good results. I don’t need the extra speed and heat that the Pro models have. I also only need drives tuned to work together in a box with 5 or less bays in it.
Check it out here: AnandTech – 6TB Western Digital RedPro HDD