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From "Bharat Viswanadham (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (HDFS-12827) Need Clarity on Replica Placement: The First Baby Steps in HDFS Architecture documentation
Date Thu, 16 Nov 2017 22:39:00 GMT

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

Bharat Viswanadham edited comment on HDFS-12827 at 11/16/17 10:38 PM:
----------------------------------------------------------------------

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}
.

http://hadoop.apache.org/docs/r3.0.0-beta1/hadoop-project-dist/hadoop-hdfs/HdfsDesign.html

Pls let me know any more is needed?


was (Author: bharatviswa):
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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