The first thing to note is the general format of these configuration files. They are obviously <br />XML and contain multiple property specifications within a single configuration element. <br />The property specifications always contain name and value elements with the possibility for <br />optional comments not shown in the preceding code. <br /> <br />We set three configuration variables here: <br /> <br />The dfs.default.name variable holds the location of the NameNode and is <br />required by both HDFS and MapReduce components, which explains why it's in <br />core-site.xml and not hdfs-site.xml. <br /> <br />The dfs.replication variable specifies how many times each HDFS block should <br />be replicated. <br /> <br />The mapred.job.tracker variable holds the location of the JobTracker just <br />like dfs.default.name holds the location of the NameNode. Because only <br />MapReduce components need know this location, it is in mapred-site.xml.
