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From "Hairong Kuang (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-3799) Design a pluggable interface to place replicas of blocks in HDFS
Date Mon, 11 May 2009 17:35:45 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-3799?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12708122#action_12708122

Hairong Kuang commented on HADOOP-3799:

> Balancer does not use the configured policy but ensures that the number of unique racks
for the block is not reduced. Thus, both these components should work ok with a externally
configured replication policy, isn't it? 
Replication policies may have other requirements other than number of racks, for example co-location.
I don't think balancer handles this right now.

> Design a pluggable interface to place replicas of blocks in HDFS
> ----------------------------------------------------------------
>                 Key: HADOOP-3799
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3799
>             Project: Hadoop Core
>          Issue Type: Improvement
>          Components: dfs
>            Reporter: dhruba borthakur
>            Assignee: dhruba borthakur
>         Attachments: BlockPlacementPluggable.txt
> The current HDFS code typically places one replica on local rack, the second replica
on remote random rack and the third replica on a random node of that remote rack. This algorithm
is baked in the NameNode's code. It would be nice to make the block placement algorithm a
pluggable interface. This will allow experimentation of different placement algorithms based
on workloads, availability guarantees and failure models.

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