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From "Wang Xu (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1312) Re-balance disks within a Datanode
Date Mon, 21 Feb 2011 08:35:39 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1312?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12997302#comment-12997302
] 

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

Hi Steve,

>From my point, there are mainly two cases of re-balance:
# The admin replace a disk, and then trigger the re-balance at once or in specific time.
# The monitoring system observed disk space distribution issue, and rise a warning; and then
the admin trigger the re-balance at once or in specific time.

Do you mean we should integrate a monitoring system inside 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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