col function_name    format a25         heading "File Type"
col reads            format 999,999,999,999  heading "Reads"
col writes           format 999,999,999,999  heading "Writes"
col number_of_waits  format 999,999,999,999  heading "Waits" 
col wait_time_sec    format 999,999,999,999 heading "Wait Time|Sec"
col avg_wait_ms      format 999.99      heading "Avg|Wait ms"
 
set lines 150
set pages 10000
 
select 
   function_name, 
   small_read_reqs + large_read_reqs reads,
   small_write_reqs + large_write_reqs writes, 
   wait_time/1000 wait_time_sec,
   case when number_of_waits > 0 then 
          round(wait_time / number_of_waits, 2)
       end avg_wait_ms
from 
   v$iostat_function
order by 
    wait_time desc;