title: Why is Hadoop MapReduce so slow and not using all of the available resources?
body: <p>I am currently testing the performance of Apache Hadoop in a 9 node cluster with each node having 4Gig RAM plus 2 CPU's and determined that when submitting a single job the resources of the cluster (RAM, CPU, NET, disk I/O) are nearly unused.</p>
  
  <p>What are the limited factors that prevent MapReduce to use all available resources?</p>