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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 Thu, 15 Nov 2012 21:29:13 GMT

    [ https://issues.apache.org/jira/browse/HDFS-3941?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13498353#comment-13498353

Tsz Wo (Nicholas), SZE commented on HDFS-3941:

> ... Can you take a look at it? ...

Sure, I have commented on HADOOP-9045.

We usually use a JIRA for a single issue/bug.  The patch can be merged/backported to earlier
branches within the same JIRA.  In this case, let's keep HDFS-3941 for backporting HDFS-3498
and HDFS-3601, and then fix the bug by HADOOP-9045 (so we will commit HADOOP-9045 to both
trunk and branch-1).  Sounds good?

BTW, if you are busy on something, Jing can help out here.
> 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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