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From "Daniel Templeton (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-1312) Re-balance disks within a Datanode
Date Mon, 05 Oct 2015 22:38:31 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1312?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14944172#comment-14944172
] 

Daniel Templeton commented on HDFS-1312:
----------------------------------------

The reporting aspect should perhaps be handled under HDFS-1121.

Given HDFS-1804, I think [~steve_l]'s original proposal of a balancer script that can be run
manually while the DN is offline sounds like a simpler/safer/better approach.  Since the primary
remaining source of imbalance is disk failure, an offline process seems sensible.  What's
the main motivation for building an online-balancer?

> 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
>         Attachments: 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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