In many applications, crashes are less of a problem than falsely believing a write happened persistently. Consider a mail server: if it can wait until the messa

In many applications, crashes are less of a problem than falsely believing a write happened persistently. Consider a mail server: if it can wait until the message is really saved before returning the final success response, then a crash means a retry later (and maybe a duplicated message if the crash happened in the small window between the write committing and the response going out) rather than a lost message.