This is a boolean parameter that controls whether writes will always be written to stable storage before the write call returns. If this is no then the server will be guided by the client's request in each write call (clients can set a bit indicating that a particular write should be synchronous). If this is yes then every write will be followed by a fsync() call to ensure the data is written to disk. Note that the strict sync parameter must be set to yes in order for this parameter to have any effect. strict sync no