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https://issues.apache.org/jira/browse/HDFS-2576?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13588678#comment-13588678
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Aaron T. Myers commented on HDFS-2576:
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Any thoughts about making these hints persistent on the NN? It looks like the
current patch would only come into play at file creation time, which means that
after the file is written DN failures or running the balancer would cause HDFS
to no longer know which DNs should be favored for the replicas of a given file.
> Namenode should have a favored nodes hint to enable clients to have control
> over block placement.
> -------------------------------------------------------------------------------------------------
>
> Key: HDFS-2576
> URL: https://issues.apache.org/jira/browse/HDFS-2576
> Project: Hadoop HDFS
> Issue Type: New Feature
> Reporter: Pritam Damania
> Attachments: hdfs-2576-1.txt
>
>
> Sometimes Clients like HBase are required to dynamically compute the
> datanodes it wishes to place the blocks for a file for higher level of
> locality. For this purpose there is a need of a way to give the Namenode a
> hint in terms of a favoredNodes parameter about the locations where the
> client wants to put each block. The proposed solution is a favored nodes
> parameter in the addBlock() method and in the create() file method to enable
> the clients to give the hints to the NameNode about the locations of each
> replica of the block. Note that this would be just a hint and finally the
> NameNode would look at disk usage, datanode load etc. and decide whether it
> can respect the hints or not.
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