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From "Aaron T. Myers (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2576) Namenode should have a favored nodes hint to enable clients to have control over block placement.
Date Wed, 27 Feb 2013 19:45:14 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2576?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13588678#comment-13588678
] 

Aaron T. Myers commented on HDFS-2576:
--------------------------------------

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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