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

["Bharat Viswanadham (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HDFS-12827?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16256077#comment-16256077 ] 

Bharat Viswanadham commented on HDFS-12827:
-------------------------------------------

Hi [~surinuthalapati@live.com]
In the latest design document, it is mentioned correctly

{code:java}
when the replication factor is three, HDFS’s placement policy is to put one replica on the local machine if the writer is on a datanode, otherwise on a random datanode, another replica on a node in a different (remote) rack, and the last on a different node in the same remote rack
{code}
.
Pls let me know any more is needed?

> Need Clarity on Replica Placement: The First Baby Steps in HDFS Architecture documentation
> ------------------------------------------------------------------------------------------
>
>                 Key: HDFS-12827
>                 URL: https://issues.apache.org/jira/browse/HDFS-12827
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: documentation
>            Reporter: Suri babu Nuthalapati
>            Priority: Minor
>
> 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.
> ############
> 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. 



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