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Date: Thu, 8 Jul 2010 18:15:57 -0400 (EDT)
From: "Rodrigo Schmidt (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Subject: [jira] Commented: (HDFS-1094) Intelligent block placement policy to
 decrease probability of block loss
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    [ https://issues.apache.org/jira/browse/HDFS-1094?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12886521#action_12886521 ] 

Rodrigo Schmidt commented on HDFS-1094:
---------------------------------------

@Konstantin: The new policy will have, for every block, a limited window of racks you can choose from, and a limited window of machines within such racks. For every block, we will keep the idea of having a copy that is local to the writer, and two copies at a remote rack, but always respecting this limited window of choices.

> 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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