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https://issues.apache.org/jira/browse/HDFS-385?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12732267#action_12732267
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Sanjay Radia commented on HDFS-385:
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>>The usage model it to define a policy for the entire cluster when you create
>>the cluster. This is especially useful when you have an HDFS instance on
>>Amazon EB2 instance for example. This is not intended to be dynamic in any
>>shape or form for a specified cluster.
>Given the above should the system record the policy in the fsImage to prevent
>it from being changed?
This is a little trickier than I originally thought. If the policy is fixed
then it should be recorded in the fsimage at creation time - indeed the policy
class name could be the policy name.
On further thinking, we may want to allow compatible policies.
So further thought is required on how to record the policy while allowing
compatible changes.
Shall we postpond the recording of the policy to another future Jira?
> 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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