- * If we have an external log device, flush the data device
- * before flushing the log to make sure all meta data
- * written back from the AIL actually made it to disk
- * before writing out the new log tail LSN in the log buffer.
+ * Flush the data device before flushing the log to make
+ * sure all meta data written back from the AIL actually made
+ * it to disk before stamping the new log tail LSN into the
+ * log buffer. For an external log we need to issue the
+ * flush explicitly, and unfortunately synchronously here;
+ * for an internal log we can simply use the block layer
+ * state machine for preflushes.