title: why did serverstatus have a bad effect on mongod write operation?
body: <p>I have 1 mongos, 3 mongod and 3 config server. when I write some documents, sometimes the insert speed of one of mongods is very slow and there're "serverstatus was very slow" in mongod log file. why?</p>
  
  <p>the version is 2.0.4</p>