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https://issues.apache.org/jira/browse/HDFS-3619?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14643679#comment-14643679
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Tsz Wo Nicholas Sze commented on HDFS-3619:
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> Does this constraint looks too strong so that slightly in-consistence with
> BlockPlacementPolicyDefault?
Yes, Balancer has a stronger constraint. Let's keep it like this so that it
can easily support a different BlockPlacementPolicy.
> isGoodBlockCandidate() in Balancer is not handling properly if replica factor
> >3
> --------------------------------------------------------------------------------
>
> Key: HDFS-3619
> URL: https://issues.apache.org/jira/browse/HDFS-3619
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: balancer & mover
> Affects Versions: 1.0.0, 2.0.0-alpha
> Reporter: Junping Du
> Assignee: Junping Du
>
> Let's assume:
> 1. replica factor = 4
> 2. source node in rack 1 has 1st replica, 2nd and 3rd replica are in rack 2,
> 4th replica in rack3 and target node is in rack3.
> So, It should be good for balancer to move replica from source node to target
> node but will return "false" in isGoodBlockCandidate(). I think we can fix it
> by simply making judgement that at least one replica node (other than source)
> is on the different rack of target node.
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