How does Hadoop's block replacement policy work?

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I'm working on a Hadoop cluster and my cluster has nodes in seven racks, and I have provided a rack topology script. What is Hadoop's block placement policy, assuming a block replication factor of three?
Aug 16, 2018 in Big Data Hadoop by Meci Matt
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In your case, One copy of the block is written to a node in one rack; two copies are written to two nodes in a different rack.
Actually, what happens is HDFS uses rack-aware replica placement policy. In default configuration there are total 3 copies of a datablock on HDFS, 2 copies are stored on datanodes on same rack and 3rd copy on a different rack.

Hope this helps!
answered Aug 16, 2018 by nitinrawat895
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