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https://issues.apache.org/jira/browse/HDFS-1312?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13480055#comment-13480055
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Steve Hoffman commented on HDFS-1312:
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Given the general nature of HDFS and its many uses (HBase, M/R, etc) as much as
I'd like it to "just work", it is clear it always depends on the use. Maybe
one day we won't need a balancer script for disks (or for the cluster).
I'm totally OK with having a machine-level balancer script. We use the HDFS
balancer to fix inter-machine imbalances when they crop up (again, for a
variety of reasons). It makes sense to have a manual script for intra-machine
imbalances for people who DO have issues and make it part of the standard
install (like the HDFS 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: 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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