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https://issues.apache.org/jira/browse/HDFS-1312?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13620835#comment-13620835
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Kevin Lyda commented on HDFS-1312:
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Are there any decent code examples for how one might do this? I've never done 
hadoop dev so some pointers for where to start would be appreciated.
                
> Re-balance disks within a Datanode
> ----------------------------------
>
>                 Key: HDFS-1312
>                 URL: https://issues.apache.org/jira/browse/HDFS-1312
>             Project: Hadoop HDFS
>          Issue Type: New Feature
>          Components: datanode
>            Reporter: Travis Crawford
>
> Filing this issue in response to ``full disk woes`` on hdfs-user.
> Datanodes fill their storage directories unevenly, leading to situations 
> where certain disks are full while others are significantly less used. Users 
> at many different sites have experienced this issue, and HDFS administrators 
> are taking steps like:
> - Manually rebalancing blocks in storage directories
> - Decomissioning nodes & later readding them
> There's a tradeoff between making use of all available spindles, and filling 
> disks at the sameish rate. Possible solutions include:
> - Weighting less-used disks heavier when placing new blocks on the datanode. 
> In write-heavy environments this will still make use of all spindles, 
> equalizing disk use over time.
> - Rebalancing blocks locally. This would help equalize disk use as disks are 
> added/replaced in older cluster nodes.
> Datanodes should actively manage their local disk so operator intervention is 
> not needed.

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