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From "Tsz Wo (Nicholas), SZE (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-3941) Backport HDFS-3498 and HDFS3601: update replica placement policy for new added "NodeGroup" layer topology
Date Tue, 13 Nov 2012 22:26:12 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3941?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13496612#comment-13496612
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Tsz Wo (Nicholas), SZE commented on HDFS-3941:
----------------------------------------------

Hi Junping, the posted patch is quite different from the ones in HDFS-3498 and HDFS3601. 
It seems that there is some code refactoring.  Could you make the patch look the same as the
ones in trunk?  For code refactoring, bug fixes or other additional works, let's do it separately
so that the changes will also go to trunk.
                
> 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: name-node
>    Affects Versions: 1.0.0
>            Reporter: Junping Du
>            Assignee: Junping Du
>         Attachments: 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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