title: HDFS' Location Awareness
body: <p><strong>Introduction</strong></p>
  
  <p>According to several documentation <a href="http://en.wikipedia.org/wiki/Apache_Hadoop" rel="nofollow">1</a>, <a href="http://cse360fall12.wikispaces.asu.edu/Apache+Hadoop" rel="nofollow">2</a>, <a href="http://hadoop.apache.org/docs/r2.3.0/hadoop-project-dist/hadoop-hdfs/HdfsUserGuide.html" rel="nofollow">3</a> HDFS' Location Awareness is about knowing the physical location of nodes and replicating data on different racks to reduce the impact of rack issues due to, e.g. power supply and/or switch issues.</p>
  
  <p><strong>Question</strong></p>
  
  <p>How does HDFS know the physical location of nodes and racks and subsequently decide to replicate data to nodes located on other racks?</p>