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https://issues.apache.org/jira/browse/HDFS-11242?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16870546#comment-16870546
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Lars Francke commented on HDFS-11242:
-------------------------------------

Specifically: What [~reidchan] can currently already be done but requires a 
restart, so the same "risk" already exists.

Does HDFS start moving data when the topolgy changes? I always was under the 
assumption that it only happens on a balance operation.

> Add refresh cluster network topology operation to dfs admin
> -----------------------------------------------------------
>
>                 Key: HDFS-11242
>                 URL: https://issues.apache.org/jira/browse/HDFS-11242
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: namenode
>    Affects Versions: 3.0.0-alpha1
>            Reporter: Reid Chan
>            Priority: Minor
>         Attachments: HDFS-11242.002.patch, HDFS-11242.patch
>
>
> The network topology and dns to switch mapping are initialized at the start 
> of the namenode.
> If admin wants to change the topology because of new datanodes added, he has 
> to stop and restart namenode(s), otherwise those new added datanodes are 
> squeezed under /default-rack.
> It is a low frequency operation, but it should be operated appropriately, so 
> dfs admin should take the responsibility.



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