[HDFS-12827] Need Clarity on Replica Placement: The First Baby Steps in HDFS Architecture documentation

• Type: Improvement
• Status: Resolved
• Priority: Minor
• Resolution: Not A Problem
• Component/s: documentation
• Assignee: Bharat Viswanadham
• Reporter: Suri Nuthalapati
• Created: 16/Nov/17 19:56
• Updated: 17/Nov/17 02:21
• Resolved: 17/Nov/17 02:21

Description

The placement should be this:
https://hadoop.apache.org/docs/r1.2.1/hdfs_design.html

HDFS’s placement policy is to put one replica on one node in the local rack, another on a node in a different (remote) rack, and the last on a different node in the same remote rack.

Hadoop Definitive guide says the same and I have tested and saw the same behavior as above.

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But the documentation in the versions after r2.5.2 it was mentioned as:
http://hadoop.apache.org/docs/r2.5.2/hadoop-project-dist/hadoop-hdfs/HdfsDesign.html

HDFS’s placement policy is to put one replica on one node in the local rack, another on a different node in the local rack, and the last on a different node in a different rack.