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From "Jingkei Ly (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-3799) Design a pluggable interface to place replicas of blocks in HDFS
Date Wed, 13 May 2009 09:46:45 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-3799?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12708862#action_12708862
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Jingkei Ly commented on HADOOP-3799:
------------------------------------

> hdfs probably needs to store metadata with the files or blocks
Instead of storing replication policy metadata with the blocks, could you keep the responsibility
for this back with the replica placement plugin-code? 

So assuming the balancer is also updated to use the block placement interface; if a cluster
has to support multiple replication policies, it could be the plugin-code's responsiblity
to decide which policy to use based on the file owner/permissions/filename for the block.
One advantage is that all the replication code for the cluster is encompassed in one place.

> 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
>            Assignee: dhruba borthakur
>         Attachments: BlockPlacementPluggable.txt
>
>
> 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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