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https://issues.apache.org/jira/browse/HDFS-1094?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12855935#action_12855935
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Brian Bockelman commented on HDFS-1094:
---------------------------------------

Hey Dhruba,

How does this change the probability?  Are you saying that P(rack r and rack 
r+1 fails) < P(rack i and rack j, i!=j) fails?  Can you sketch out 
mathematically how this decreases the probability of failure?

Brian

> Intelligent block placement policy to decrease probability of block loss
> ------------------------------------------------------------------------
>
>                 Key: HDFS-1094
>                 URL: https://issues.apache.org/jira/browse/HDFS-1094
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: name-node
>            Reporter: dhruba borthakur
>            Assignee: dhruba borthakur
>
> The current HDFS implementation specifies that the first replica is local and 
> the other two replicas are on any two random nodes on a random remote rack. 
> This means that if any three datanodes die together, then there is a 
> non-trivial probability of losing at least one block in the cluster. This 
> JIRA is to discuss if there is a better algorithm that can lower probability 
> of losing a block.

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