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From "Hairong Kuang (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-3799) Design a pluggable interface to place replicas of blocks in HDFS
Date Tue, 12 May 2009 17:37:45 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-3799?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12708525#action_12708525
] 

Hairong Kuang commented on HADOOP-3799:
---------------------------------------

> I would like to leave this for a future time
I do not think ignoring balancer in this design is a good idea. Yahoo runs balancer almost
24/7 on all clusters. We do not want balancer to break any of the favorite block placement
policy configured on the cluster.

Dhruba, I think this jira makes a big change to the core of DFS. It's non-trival at all. If
we ever want to make this change, we should have a design document first, explaining the semantic
of pluggable placement policy and how all block placement related components should change
to support the feature.

> 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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