title: How do I profile disk I/O within a PHP script?
body: <p>I am running 5 instances of a PHP script using <a href="http://supervisord.org/index.html" rel="nofollow">Supervisord</a>.  Running 5 processes is the optimal number to maximize the processing that my PHP script does.  If I run more than 5 or less than 5, I get worse results.</p>
  
  <p>I'm already profiling the PHP script itself with <a href="http://xdebug.org/" rel="nofollow">xdebug</a> and <a href="http://code.google.com/p/webgrind/" rel="nofollow">webgrind</a>.</p>
  
  <p>I suspect that disk I/O is what's preventing me from running more parallel processes as my CPU and Memory are not maxed out with 5 processes running.  I have 4 virtual cores on an Amazon EC2 instance, and neither Mysqld nor Supervisord are using more than 50% CPU at any given time.</p>
  
  <p>How does one profile disk I/O on a Linux Cent OS machine ( does this sound like the culprit )?</p>
  
  <p>What other bottlenecks should I be looking for?</p>
  
  <p><strong>--SOLUTION--</strong></p>
  
  <p>I was unable to find any simple solutions that gave me very in depth information.  I'm not exactly sure what I'm looking for though, so I apologize for this question and answer being vague.</p>