+.It Dv F_FULLFSYNC
+Does the same thing as
+.Xr fsync 2
+then asks the drive to
+flush all buffered data to
+the permanent storage device
+.Fa ( arg
+is ignored).
+This is currently implemented on HFS, MS-DOS (FAT),
+and Universal Disk Format (UDF) file systems.
+The operation may take quite a while to complete.
+Certain FireWire drives have also been known
+to ignore the request to flush their buffered data.