Sorry, I don't fully understand the question. If I ssh to the router and execute 'nvram show' it gives me a crapload of data. On the GUI I see 176MB free.
I have an ASUS RT-AC66U with Merlin firmware that is behind another router with its own subnet. The main router is 192.168.0.1/24 and the Asus is 192.168.2.0/23 everything works fine but whenever I try to manually assign an IP the router just sits in "Applying Settings ..." and never actually...