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https://issues.apache.org/jira/browse/HDFS-1312?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15012448#comment-15012448
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Tsz Wo Nicholas Sze commented on HDFS-1312:
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Some more comments:
- Similar to Balancer, we need to define a threshold so that the storage is
considered as balanced if its dfsUsedRatio is within nodeWeightedMean +/-
threshold.
- DataTransferProtocol.replaceBlock does support move blocks across storage
types within the same node. We only need to slightly modify it for disk
balancing (i.e. moving block within the same storage type in the same node.)
> 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
> Assignee: Anu Engineer
> Attachments: Architecture_and_testplan.pdf, 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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