db file async I/O submit

 Hi All, 

I have a database at the moment where i am seeing long waits for db file async I/O submit 

It's and 11.2.0.3 database on RHL 5.

The databae is pretty write intensive. 

An AWR for a busy period shows db file async I/O submit  as the top Background wait with long wait times. 

e.g. 

                                                             Avg

                                        %Time Total Wait    wait    Waits   % bg

Event                             Waits -outs   Time (s)    (ms)     /txn   time

-------------------------- ------------ ----- ---------- ------- -------- ------

db file async I/O submit            391     0        389     995      0.0   65.1

This is for a 15 minute snapshot. 

I'm not familiar with this event and have not had much luck searching for information. Any pointers on how to address this would be extrementl gratefully received.