title: linux IOSTAT double counting AIO write operations?
body: <p>As part of debugging an IO generator, I've run across an odd set of results under RH 6.4 running on x64 hardware (validated on multiple systems):</p>
  
  <p>-- The application uses linux async IO (i.e., non-posix) to access raw disk partitions (/dev/sdb1, O_DIRECT), and is run as root</p>
  
  <p>-- The application reports 100 io/s, and 60% writes.</p>
  
  <p>-- strace of the application reports 100 calls per second to io_submit() and io_getevents(), reflecting 100 AIO operations per second</p>
  
  <p>-- 'dstat --aio' shows 100 ops per second</p>
  
  <p>-- iostat reports 40 reads/sec, as expected, but 120 writes/second, twice as many as expected</p>
  
  <p>-- An earlier implementation, using synchronous IO, does not show "doubled" writes</p>
  
  <p>Is this behavior a known bug?</p>