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https://issues.apache.org/jira/browse/HDFS-2171?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13068028#comment-13068028
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Aaron T. Myers commented on HDFS-2171:
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Just thinking out loud - another option would be to amend the DN to use the
{{Reconfigurable}} interface to allow this setting to be changed in the DNs at
run time.
Is this not also an issue on trunk? If so, this work should probably be done
there and then back-ported to 0.20.205.
> Changes to balancer bandwidth should not require datanode restart.
> ------------------------------------------------------------------
>
> Key: HDFS-2171
> URL: https://issues.apache.org/jira/browse/HDFS-2171
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: balancer, data-node
> Affects Versions: 0.20.205.0
> Reporter: Eric Payne
> Assignee: Eric Payne
> Fix For: 0.20.205.0
>
>
> Currently in order to change the value of the balancer bandwidth
> (dfs.datanode.balance.bandwidthPerSec), the datanode daemon must be restarted.
> The optimal value of the bandwidthPerSec parameter is not always (almost
> never) known at the time of cluster startup, but only once a new node is
> placed in the cluster and balancing is begun. If the balancing is taking too
> long (bandwidthPerSec is too low) or the balancing is taking up too much
> bandwidth (bandwidthPerSec is too high), the cluster must go into a
> "maintenance window" where it is unusable while all of the datanodes are
> bounced. In large clusters of thousands of nodes, this can be a real
> maintenance problem because these "mainenance windows" can take a long time
> and there may have to be several of them while the bandwidthPerSec is
> experimented with and tuned.
> A possible solution to this problem would be to add a -bandwidth parameter to
> the balancer tool. If bandwidth is supplied, pass the value to the datanodes
> via the OP_REPLACE_BLOCK and OP_COPY_BLOCK DataTransferProtocol requests.
> This would make it necessary, however, to change the DataTransferProtocol
> version.
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