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https://issues.apache.org/jira/browse/HDFS-1312?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12996487#comment-12996487
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Steve Loughran commented on HDFS-1312:
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HDFS-1362 and this issue are part of the HDFS-664 problem "support efficient
hotswap".
Before worrying about this one, consider HDFS-1121, which is provide a way to
monitor the distribution (i.e. web view). That web/management view would be how
we'd test the rebalancing works, so its a pre-req. Also it's best to keep the
issues independent (where possible), so worry about getting HDFS-1362 in first
before trying to extend it.
That said, because the #of HDDs/server is growing to 12 or more 2TB/unit, with
3TB on the horizon, we will need this feature in the 0.23-0.24 timeframe.
> 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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