journalLatencyTest is an administrative command that tests the length of time required to write and perform a file system sync (e.g. fsync) for a file in the journal directory. You must issue the journalLatencyTest command against the admin database in the form:
{ journalLatencyTest: 1 }
The value (i.e. 1 above), does not affect the operation of the command.
注解
_journalLatencyTest is an internal command that is not enabled by default. _journalLatencyTest must be enabled by using --setParameter enableTestCommands=1 on the mongod command line. _journalLatencyTest cannot be enabled during run-time.