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Date: Fri, 18 Feb 2011 17:19:38 +0000 (UTC)
From: "Wang Xu (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
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Subject: [jira] Commented: (HDFS-1312) Re-balance disks within a Datanode
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    [ https://issues.apache.org/jira/browse/HDFS-1312?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12996525#comment-12996525 ] 

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

Hi Steve,

I have not understood the nessesary of HDFS-1121. IMHO, you can monitor the file distribution among disks with external tools such as ganglia, is it required to integrate it in the Web interface of HDFS?

I think the regular routine is finding the problem in cluster management system and then trigger the rebalance action in HDFS. 

> 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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