The data should be stored in a raw format from the different source systems. More importantly, the data stored should be immutable in nature. By making it immutable, it inherently takes care of human fault tolerance to at least some extent and takes away errors with regards to data loss and corruption. It allows data to be selected, inserted, and not updated or deleted. To cater to fundamental fast processing/performance, the data is usually stored in a denormalized fashion. Data being immutable makes the system in general simpler and more manageable.