Per the Linux man page, file create is durable when fsync is done for a file descriptor open on the directory. This makes sure the new directory entry is forced to disk.

Unplanned reboots can cause files to disappear when using ext-2. The advice on the man page is very dependent on file system behavior. WT doesn't implement the advice of the man page. FWIW neither does LevelDB.

http://linux.die.net/man/2/fsync