So after a little research, I learned that people where having success with 8GB Crucial 16GB PC3-12800 DDR3L memory; which is Unbuffered, ECC, non-registered RAM. I also learned that this device, despite the specs on Netgear's site, actually has 2 memory slots, allowing you to upgrade to 16GB, with little effort.
Well, after I got my parts in, I realized it was a little more than a small effort, because the RAM slots are not easy to get to. I read some helpful descriptions on one forum, but no one posted pictures of the process. I figured I would here.
Below is the instructions for adding memory to a ReadyNAS 516 NAS as well as pictures of the inside of a dissasembled RN516 NAS. Please note, adding Ram WILL void you warranty.
1.) Here is the RN516 box with the outer case removed. If you can't figure out how to remove the case, you probably should not proceed any further with this attempt. 7 screws on the back of the of the unit and slide the case backwards to remove.
Random pictures of the inside of a Readynas 516
2.) Now, while still in an upright position, spin it around so the metal backplane is towards you. Remove the 4 nut/screws in the corners of the backplane. Mine were black. The picture below shows them removed.
In this article:
Pictures of inside of ReadyNas 516
Netgear ReadyNas 516
Crucial 2 x 8GB Ram (16 GB Kit)