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https://issues.apache.org/jira/browse/HDFS-9355?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15031381#comment-15031381
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Surendra Singh Lilhore commented on HDFS-9355:
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Thansk [~nijel] for suggestion.
bq. One option is to give a client API to get the DNs based on storage policy.
Its good idea, user can select favored node based on his choice.
We will wait for others suggestion, if no new suggestion I will change the jira
title based on your suggestion...
> Support colocation in HDFS.
> ---------------------------
>
> Key: HDFS-9355
> URL: https://issues.apache.org/jira/browse/HDFS-9355
> Project: Hadoop HDFS
> Issue Type: New Feature
> Components: hdfs-client
> Reporter: Surendra Singh Lilhore
> Assignee: Surendra Singh Lilhore
>
> Through this feature client can give suggestion to HDFS to write his all the
> blocks on same set of datanodes. Currently this we can achieve through
> HDFS-2576. HDFS-2576 give option to hint namenode about favored nodes, but in
> heterogeneous cluster this will not work out. Support client wants to write
> his data in directory which have COLD policy, but he don't know which DN have
> ARCHIVE storage, So he will not able to give favoredNodes list.
> *Implementation*
> Colocation can enable by setting "dfs.colocation.enable" true in client
> configuration. If colocation is enable and favoredNodes list is empty then
> {{DataStreamer}} will set first set of datanodes as favoredNodes which is
> chosen for first block and subsequent block will use the same datanodes for
> write. Before closing file client can get the favoredNodes list and same he
> can use for writing new file.
>
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