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https://issues.apache.org/jira/browse/HDFS-8826?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14691417#comment-14691417
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Tsz Wo Nicholas Sze commented on HDFS-8826:
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I suggest to add an option to specify the source node list. Then, balancer
only selects blocks to move from those nodes.
> Balancer may not move blocks efficiently in some cases
> ------------------------------------------------------
>
> Key: HDFS-8826
> URL: https://issues.apache.org/jira/browse/HDFS-8826
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: balancer & mover
> Reporter: Tsz Wo Nicholas Sze
> Assignee: Tsz Wo Nicholas Sze
>
> Balancer is inefficient in the following case:
> || Datanode || Utilization || Rack ||
> | D1 | 95% | A |
> | D2 | 30% | B |
> | D3, D4, D5 | 0% | B |
> The average utilization is 25% so that D2 is within 10% threshold. However,
> Balancer currently will first move blocks from D2 to D3, D4 and D5 since they
> are under the same rack. Then, it will move blocks from D1.
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