[jira] Commented: (HADOOP-3799) Design a pluggable interface to place replicas of blocks in HDFS

["dhruba borthakur (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HADOOP-3799?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12645695#action_12645695 ] 

dhruba borthakur commented on HADOOP-3799:
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Another alternative would be to allow an application to specify that a set of files have the same "block affinity". HDFS will try to allocate blocks of these files in a few set of datanode(s).

> Design a pluggable interface to place replicas of blocks in HDFS
> ----------------------------------------------------------------
>
>                 Key: HADOOP-3799
>                 URL: https://issues.apache.org/jira/browse/HADOOP-3799
>             Project: Hadoop Core
>          Issue Type: Improvement
>          Components: dfs
>            Reporter: dhruba borthakur
>
> The current HDFS code typically places one replica on local rack, the second replica on remote random rack and the third replica on a random node of that remote rack. This algorithm is baked in the NameNode's code. It would be nice to make the block placement algorithm a pluggable interface. This will allow experimentation of different placement algorithms based on workloads, availability guarantees and failure models.

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