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https://issues.apache.org/jira/browse/HDFS-3941?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13604534#comment-13604534
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Harsh J commented on HDFS-3941:
-------------------------------
This change did not go into any branch-2 release (but is in trunk) but has made
it to branch-1, which is a feature regression between the two lines. Can it be
backported to branch-2 after discussion as well, or removed from branch-1 if
disagreed upon?
> Backport HDFS-3498 and HDFS3601: update replica placement policy for new
> added "NodeGroup" layer topology
> ---------------------------------------------------------------------------------------------------------
>
> Key: HDFS-3941
> URL: https://issues.apache.org/jira/browse/HDFS-3941
> Project: Hadoop HDFS
> Issue Type: New Feature
> Components: namenode
> Affects Versions: 1.0.0
> Reporter: Junping Du
> Assignee: Junping Du
> Fix For: 1.2.0, 1-win
>
> Attachments: HDFS-3941.002.patch, HDFS-3941.003.patch,
> HDFS-3941.004.patch, HDFS-3941.005.patch, HDFS-3941.patch
>
>
> With enabling additional layer of "NodeGroup", the replica placement policy
> used in BlockPlacementPolicyWithNodeGroup is updated to following rules:
> 0. No more than one replica is placed within a NodeGroup (*)
> 1. First replica on the local node.
> 2. Second and third replicas are within the same rack but remote rack with
> 1st replica.
> 3. Other replicas on random nodes with restriction that no more than two
> replicas are placed in the same rack, if there is enough racks.
> Also, this patch abstract Replica Removal Policy from FSNameSystem to
> BlockPlacementPolicy and update removal policy slightly to remove duplicated
> replica within the same NodeGroup first when over-replicated happens.
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