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From "Tsz Wo Nicholas Sze (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-8204) Balancer: 2 replicas ends in same node after running balance.
Date Wed, 22 Apr 2015 22:06:59 GMT

    [ https://issues.apache.org/jira/browse/HDFS-8204?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14508017#comment-14508017
] 

Tsz Wo Nicholas Sze commented on HDFS-8204:
-------------------------------------------

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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