I was wondering is NETGEAR going to release a firmware upgrade to make this unit support more then 4TB disks and more then 16TB total size.
That was taken care of a long time ago (6.4.0 firmware, released in October 2015). The hardware compatibility list for the RN104 includes drives up to 12 TB in size.
The performance of this NAS is limited by it's CPU and memory, and if you create larger volumes the resync time will get longer. A resync requires every block in the data volume to either be read or written (whether it is used or not).
