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https://issues.apache.org/jira/browse/HDFS-1312?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13479689#comment-13479689
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Kevin Lyda commented on HDFS-1312:
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As an alternative, this issue could be avoided if clusters were configured with
LVM and data striping. Well, not avoided, but with the problem pushed down a
layer. However tuning docs discourage using LVM.
Besides performance, another obvious downside to putting a single fs across all
disks is that a single disk failure would destroy the entire node as opposed to
a portion of it. However I'm new to hadoop so am not sure how a partial data
loss event is handled. If a data node w/ a partial data loss can be restored
w/o copying in the data it has not lost, then avoiding striped LVM is a huge
win. Particularly for the XX TB case mentioned above where balancing in a new
node from scratch would involve a huge data transfer with time and network
consequences.
> 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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