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https://issues.apache.org/jira/browse/HDFS-8204?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14508017#comment-14508017
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Tsz Wo Nicholas Sze commented on HDFS-8204:
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The problem is actually that two replicas will be scheduled to be moved to the
same node. The first replica will be moved to the node successfully but the
second replica move will fail since there is already a replica in the node.
Therefore the bug will NOT decrease the number of replicas. It only makes
balancer scheduling inefficient.
[~walter.k.su], do you agree?
> Balancer: 2 replicas ends in same node after running balance.
> -------------------------------------------------------------
>
> Key: HDFS-8204
> URL: https://issues.apache.org/jira/browse/HDFS-8204
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: balancer & mover
> Reporter: Walter Su
> Assignee: Walter Su
> Attachments: HDFS-8204.001.patch
>
>
> Balancer moves blocks between Datanode(Ver. <2.6 ).
> Balancer moves blocks between StorageGroups ( introduced by HDFS-6584) , in
> the new version(Ver. >=2.6) .
> function
> {code}
> class DBlock extends Locations<StorageGroup>
> DBlock.isLocatedOn(StorageGroup loc)
> {code}
> is flawed, may causes 2 replicas ends in same node after running balance.
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