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https://issues.apache.org/jira/browse/HDFS-1094?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12885848#action_12885848
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Hairong Kuang commented on HDFS-1094:
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Rodrigo, thanks for your explanation. Now I understand your proposal much
better.
> We assume machine failures are independent.
I am not sure if I agree with this assumption. From the attached analysis, the
in-rack placement has the lowest data loss probability. This is
counter-intuitive. in reality, the chance of losing a rack is not small. So a
block placement policy normally place a block in at least two racks.
> 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: Rodrigo Schmidt
> Attachments: prob.pdf, prob.pdf
>
>
> 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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