How does bitrot protection actually work?

sgogo wrote:

Just so I am clear, the process would be that the bit rot protection routine first checks the primary data, then, if it finds an error, it goes out to the redundant data location and checks THAT data. It will only write from the redundant location to the original location if it finds a correct checksum at the redundant location. If it finds an incorrect checksum at both locations (it will find both locations incorrect, since the memory is defective) then no data is written and an error is generated. This is the way the ZFS system works and inspires confidence. Do I have it correct?