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https://issues.apache.org/jira/browse/HDFS-15896?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Yang Yun updated HDFS-15896:
----------------------------
    Attachment: HDFS-15896.001.patch
        Status: Patch Available  (was: Open)

> Add used percert limitation to BlockPlacementPolicyDefault for choosing 
> DataNode  to write
> ------------------------------------------------------------------------------------------
>
>                 Key: HDFS-15896
>                 URL: https://issues.apache.org/jira/browse/HDFS-15896
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: block placement
>         Environment: {code:java}
>  {code}
>            Reporter: Yang Yun
>            Assignee: Yang Yun
>            Priority: Minor
>         Attachments: HDFS-15896.001.patch
>
>
> Add used percent limitation to BlockPlacementPolicyDefault for choosing 
> datanode to write.
> The logical is similar with avoid stale node.
> Default is disable, the high used percent is 100.0%
> {code:java}
> public static final String 
>  DFS_NAMENODE_HIGH_USED_DATANODE_FOR_WRITE_PERCENT_KEY =
>  "dfs.namenode.high-used.datanode.for.wirte.percent";
> public static final float
>  DFS_NAMENODE_HIGH_USED_DATANODE_FOR_WRITE_PERCENT_DEFAULT =
>  100.0f;{code}
> The choosing will try two times, if the first failed for high used datanode, 
> it will try again without high used limitation.
> Also add a high  used ratio,  when the percentage of high used datanodes 
> reaches this ratio, allow writing to high used nodes to prevent hotspots.
> {code:java}
> public static final String
>  DFS_NAMENODE_HIGH_USED_DATANODE_FOR_WRITE_RATIO_KEY =
>  "dfs.namenode.high-used.datanode.for.wirte.ratio";
> public static final float
>  DFS_NAMENODE_HIGH_USED_DATANODE_FOR_WRITE_RATIO_DEFAULT = 0.6f;{code}
>  



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