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https://issues.apache.org/jira/browse/HDFS-385?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12729479#action_12729479
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Robert Chansler commented on HDFS-385:
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Experiments with replica placement are important, and I want to read the
resulting papers. But a production implementation of an alternate policy has
implications beyond just writing a class that implements a new interface.
Perhaps we need something like a [Black Box
Warning|http://en.wikipedia.org/wiki/Black_box_warning] to remind folk that
using this feature to store real bytes is:
* Dangerous
* Really dangerous
* Not something that will be supported in the future if it stands in the way of
other development
* Not something where others can be expected to volunteer help either to
relieve the dangers or cope with the consequences.
> Design a pluggable interface to place replicas of blocks in HDFS
> ----------------------------------------------------------------
>
> Key: HDFS-385
> URL: https://issues.apache.org/jira/browse/HDFS-385
> Project: Hadoop HDFS
> Issue Type: Improvement
> Reporter: dhruba borthakur
> Assignee: dhruba borthakur
> Fix For: 0.21.0
>
> Attachments: BlockPlacementPluggable.txt,
> BlockPlacementPluggable2.txt, BlockPlacementPluggable3.txt,
> BlockPlacementPluggable4.txt, BlockPlacementPluggable4.txt,
> BlockPlacementPluggable5.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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