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https://issues.apache.org/jira/browse/HDFS-12827?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16256077#comment-16256077
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Bharat Viswanadham edited comment on HDFS-12827 at 11/16/17 10:38 PM:
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Hi [~surinuthalap...@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 [~surinuthalap...@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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