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https://issues.apache.org/jira/browse/HDFS-16974?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17709976#comment-17709976
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ASF GitHub Bot commented on HDFS-16974:
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zhangshuyan0 opened a new pull request, #5541:
URL: https://github.com/apache/hadoop/pull/5541

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   ### Description of PR
   The current target choosing policy only considers the load of the entire 
datanode. If both DN1 and DN2 have an `xceiverCount` of 100, but DN1 has 10 
volumes to write to and DN2 only has 1, then the pressure on DN2 is actually 
much greater than that on DN1. This patch has added a configuration that allows 
us to avoid nodes with too much pressure on a single volume when choosing 
targets, so as to avoid overloading datanodes with few volumes or slowing down 
writes.
   
   ### How was this patch tested?
   Add a new UT for this.




> Consider load of every volume when choosing target
> --------------------------------------------------
>
>                 Key: HDFS-16974
>                 URL: https://issues.apache.org/jira/browse/HDFS-16974
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>            Reporter: Shuyan Zhang
>            Assignee: Shuyan Zhang
>            Priority: Major
>
> The current target choosing policy only considers the load of the entire 
> datanode. If both DN1 and DN2 have an `xceiverCount` of 100, but DN1 has 10 
> volumes to write to and DN2 only has 1, then the pressure on DN2 is actually 
> much greater than that on DN1. This patch has added a configuration that 
> allows us to avoid nodes with too much pressure on a single volume when 
> choosing targets, so as to avoid overloading datanodes with few volumes or 
> slowing down writes.



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