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From "Steve Loughran (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-1312) Re-balance disks within a Datanode
Date Thu, 27 Sep 2012 09:10:14 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1312?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13464564#comment-13464564
] 

Steve Loughran commented on HDFS-1312:
--------------------------------------

Let's start with a python script that people can use while the DN is offline, as that would
work against all versions. Moving as a background task would be much better -but I can imagine
surprises (need to make sure block isn't in use locally, remotely, handling of very unbalanced
disks (where disk #4 is a 50TB NFS mount, etc).
                
> 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: data-node
>            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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