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https://issues.apache.org/jira/browse/HADOOP-3799?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12707426#action_12707426
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Hairong Kuang commented on HADOOP-3799:
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Dhruba, what's the implication of a pluggable block placement policy to
balancer, under-replicated, and over-replicated blocks? Currently they all
assumes there is only one replication policy. Is it possible that a block is
created with one replication policy and then later in its life use a different
policy to handle its over/under-replicaton and balancing? Or we need to persist
their initial placement policy on disk.
> 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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