Hi,
As much as one would like to view your constant architectural questions with a positive awe of your curiosity, I think you are going to get neither in-depth technical descriptions (these are technical trade secrets, to some extent) nor long, involved "NetApp for Dummies" type of explanations here. If your interest is genuine, then you will need to do a bit more of your own searching and researching.
The architectures of the different series of NetApps throughout the years have simultaneously used both ECC and NVRAM for different purposes.