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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-3799) Design a pluggable interface to place replicas of blocks in HDFS
Date Sun, 10 May 2009 11:13:45 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-3799?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12707779#action_12707779
] 

dhruba borthakur commented on HADOOP-3799:
------------------------------------------

@Hairong: fsck uses verifyReplication() to ensure whether replicaas are placed according to
the configured policy, and this method is part of the proposed BlockPlacement policy interface.
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?




> 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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