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Date: Thu, 16 Nov 2017 22:39:00 +0000 (UTC)
From: "Bharat Viswanadham (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Message-ID: <JIRA.13119021.1510862203000.260017.1510871940236@Atlassian.JIRA>
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Subject: [jira] [Comment Edited] (HDFS-12827) Need Clarity on Replica
 Placement: The First Baby Steps in HDFS Architecture documentation
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archived-at: Thu, 16 Nov 2017 22:39:05 -0000


    [ https://issues.apache.org/jira/browse/HDFS-12827?page=3Dcom.atlassian=
.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=3D1625=
6077#comment-16256077 ]=20

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=E2=80=99s placement policy is to=
 put one replica on the local machine if the writer is on a datanode, other=
wise 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=E2=80=99s placement policy is to=
 put one replica on the local machine if the writer is on a datanode, other=
wise 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 Architect=
ure 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:=20
> https://hadoop.apache.org/docs/r1.2.1/hdfs_design.html
> HDFS=E2=80=99s 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/Hdfs=
Design.html
> HDFS=E2=80=99s 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.=20


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