There was a pretty good discussion on this particular thread: https://news.ycombinator.com/item?id=3173993
The redundant business logic processing should be happening in parallel continuously with the results being verified identical.
This type of system has the added benefit of continuously checking for hardware failure by checking against multiple execution units.
There was a pretty good discussion on this particular thread: https://news.ycombinator.com/item?id=3173993