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From "Wang Xu (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1312) Re-balance disks within a Datanode
Date Fri, 04 Mar 2011 04:04:37 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1312?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13002437#comment-13002437
] 

Wang Xu commented on HDFS-1312:
-------------------------------

Hi Allen,

For the cluster monitoring issue, we could not expect an integrated monitoring substitute
the external monitoring system. Thus, we need to make clear what information gathering requirements
should be considered inside hdfs.

And the "lock" I mentions is to stop write new blocks into the volume, which is the simplest
way to migrate blocks. And I do think the depth is matter, from my understanding, the deeper
the dir is, the more io will be wasted to reach the block.  

> 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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