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Namenode and DataNode Communication





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Say File1.txt is the file which needs to be stored in HDFS.This file is splited up to blocks A, C of size 64 MB(default size,can be modified) .These blocks are stored in different datanodes and the information about these blocks i.e the metadata about these blocks is stored in namenode.

When a new block comes in ,how does the namenode know which datanode to place that block?.
For this ,there is a communication which happens between Namenode and datanode.  

  • Data node sends heartbeats every 3 seconds via a TCP handshake
  • ÄEvery 10thheart beat is a block report
  • ÄNamenode builds metadata from block report
  • ÄCommunication happens through the port defined for Namenode 
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- See more at: http://labstrikes.blogspot.in/2012/08/adsense-middle-blog-post.html#sthash.gQgSkqx8.dpuf
 
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