I see where you are headed but that is bad logic. It is like saying your car may catch on fire anytime or a meteorite can strike so why bother also wearing a seat belt?

Sorry you cannot possibly defend un-acknowledged writes as a default setting on a product that calls itself a database. Saying you need 3 machines anyway.

By coming up with more arguments and excuses as a defense for this design you are actually making the product you are defending look worse.

i didn't mean to imply that. i do agree that your db client should check for write errors if you care about your data, and that mongodb should make their official drivers have safer defaults.

but the poster to which i was replying seemed to be saying that machine redundancy was somehow optional. it is not. hardware fails, and the architecture of whatever db server you are using is irrelevant when it does.