> This interpretation hinges on interpreting successful sub-majority writes as not necessarily successful: rather, a successful response is merely a suggestion that the write has probably occurred, or might later occur, or perhaps will occur, be visible to some clients, then un-occur, or perhaps nothing will happen whatsoever.

> We note that this remains MongoDB’s default level of write safety.

This sounds pretty scary. How does it compare to other distributed dbs, like Riak? My understanding is that Riak lets you specify how many nodes a write must succeed on to be considered successful. Are its responses more reliable? Is this just a "distributed computing is hard" situation?