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https://issues.apache.org/jira/browse/HDFS-2171?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13071223#comment-13071223
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Eric Payne commented on HDFS-2171:
----------------------------------

Hadoop QA PreCommitHDFS-Build is trying to apply patch to trunk. That is why 
the auto build failed.

Here is the output of the test-patch process which I ran in my build 
environment:

     [exec] BUILD SUCCESSFUL
     [exec] Total time: 5 minutes 31 seconds
     [exec] 
     [exec] 
     [exec] 
     [exec] 
     [exec] +1 overall.  
     [exec] 
     [exec]     +1 @author.  The patch does not contain any @author tags.
     [exec] 
     [exec]     +1 tests included.  The patch appears to include 6 new or 
modified tests.
     [exec] 
     [exec]     +1 javadoc.  The javadoc tool did not generate any warning 
messages.
     [exec] 
     [exec]     +1 javac.  The applied patch does not increase the total number 
of javac compiler warnings.
     [exec] 
     [exec]     +1 findbugs.  The patch does not introduce any new Findbugs 
(version 1.3.9) warnings.
     [exec] 
     [exec] 
     [exec] 
     [exec] 
     [exec] 
======================================================================
     [exec] 
======================================================================
     [exec]     Finished build.
     [exec] 
======================================================================
     [exec] 
======================================================================
     [exec] 
     [exec] 

BUILD SUCCESSFUL
Total time: 14 minutes 33 seconds


> 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
>
>         Attachments: HDFS-2171.patch
>
>
> 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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