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From "Anu Engineer (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-1312) Re-balance disks within a Datanode
Date Thu, 19 Nov 2015 00:40:11 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1312?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15012479#comment-15012479
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Anu Engineer commented on HDFS-1312:
------------------------------------

bq. Yes. Mean and variance are well known concepts. It is easier for other people to understand
the feature and read the matrices/reports. They don't have to look up what does it mean by
"data density".

Thanks, I will update the patch with that change. The current patch in HDFS-9420 contains
notions of "data density".



> 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
>            Assignee: Anu Engineer
>         Attachments: Architecture_and_testplan.pdf, disk-balancer-proposal.pdf
>
>
> 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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