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From "Allen Wittenauer (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-11676) Add API to NetworkTopology for getting all racks
Date Thu, 05 Mar 2015 15:23:39 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-11676?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14348861#comment-14348861
] 

Allen Wittenauer commented on HADOOP-11676:
-------------------------------------------

What happens when more racks appear dynamically due to HDFS expansion?

> Add API to NetworkTopology for getting all racks
> ------------------------------------------------
>
>                 Key: HADOOP-11676
>                 URL: https://issues.apache.org/jira/browse/HADOOP-11676
>             Project: Hadoop Common
>          Issue Type: Sub-task
>            Reporter: Walter Su
>            Assignee: Walter Su
>
> The existing two NetworkTopology.chooseRandom(..) API support choosing node from scope
and choosing outside scope. BlockPlacementPolicyDefault class use these two API to choose
node from one rack or choose outside one rack.
> We want to implement a new placement policy called BlockPlacementPolicyFaultTolerant
which tries its best to place replicas to most racks. To achieve this, We need to know how
many replicas each rack has. And first, we need to get all racks.



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