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https://issues.apache.org/jira/browse/HDFS-385?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12729453#action_12729453
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dhruba borthakur commented on HDFS-385:
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I agree that that this API might have to evolve over time. We should mark it as
"unstable" in bold letters.
> In the past folks have complained that hadoop is too easy to misconfigure.
The default policy should work well for 99/9% people out there. Only a system
admin can change the default policy. And one has to write Java code to
implement a new policy... making it even tougher for most people to change
policy.
>Given the above should the system record the policy in the fsImage to prevent
>it from being changed? Similarly should the balancer check to see if it has
>the same policy as the NN?
This can be done. This is mostly to reduce configuration errors, right? If so,
can we defer it till we see it being a problem?
> However the experimentation is useful and as long it does not impact the base
> code in a negative way, we should be able to add such features to hadoop
> after careful review.
Thanks. Please review the code and provide some feedback if you so desire.
> 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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