Five Hadoop Daemons

Hadoop is comprised of five separate daemons:

NameNode
--Holds the metadata for HDFS

Secondary NameNode
--Performs housekeeping functions for the NameNode
--Is not a backup or hot standby for the NameNode!

DataNode
--Stores actual HDFS data blocks

JobTracker
--Manages MapReduce jobs, distributes individual tasks to…

TaskTracker
--Responsible for instantiating and monitoring individual Map and Reduce tasks

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