For jData on the cloud, MongoDB is mainly used for persistence mainly due to the fact that its support for schema-less structure, rich indexing for query support, and scalability. While each jNode on the fog has their own Redis instance running, analytics is done on a centralized persistence data in MongoDB on the cloud. While Redis can be used as a database on its own, it is limiting for it to be used as a centralized database on the cloud since it is in-memory database, RAM size is a condition to be considered and meanwhile analytics in Lua might be tedious. However, in the architect, there is still an instance of Redis running on the cloud jNode for caching.
Here is a quick showcase of a project I have been playing around with recently. An Midi Control Pad installed on SG being synced with an arduino.