title: Hadoop - Restart datanode and tasktracker
body: <p>I want to bring down a single datanode and tasktracker, so that some new changes that i've made in my mapred-site.xml take effect, such as mapred.reduce.child.java.opts etc. How do I do that? However I don't want to bring down the whole cluster since i have active jobs running.</p>
  
  <p>Also, how can that be done ensuring that the namenode does not copy the relevant data blocks of a "temporarily down" datanode onto another node</p>