I was looking at this, "Testing Distributed Systems w/ Deterministic Simulation" by Will Wilson - YouTube, talk on You Tube concerning deterministic simulation for testing. This seems very interesting. I can see how mocking out networking would work since networking is just communication with some chaos added in. But disk I/O actually needs to write bytes at some point and probably needs to read them back. Just writing into memory limits the scale of a test. So what do you do about disk I/O? Can anyone point me a the relevant parts of the foundation DB code that implements this?