It's more interesting to see how they recover in case of failure, rather than how write is completely on disk. Machine failure will happen. Writes will not be fully flushed to disk. It's how one recovers from failure that defines how robust the system is.
Gotta say, as a database developer, this is what interests me as well. Let's assume you've had a datacenter-wide power failure, and you're running the repair process on your master and slaves -- what does that look like? How long does it take? What are the factors that influence whether or not it will complete successfully?
