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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1094) Intelligent block placement policy to decrease probability of block loss
Date Tue, 29 Jun 2010 18:13:56 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1094?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12883632#action_12883632
] 

dhruba borthakur commented on HDFS-1094:
----------------------------------------

@Koji: we have files with replication factor of 3. if a large number of datanodes fail at
the same time, we do see missing blocks. Sometimes, the datanode process on these machines
fail to start even after repeated start-dfs.sh attempts, sometimes the entire machine fails
to reboot. Then we have to manually fix a few of those bad datanode machines and make them
come online; this fixes the "missing blocks" problem but is a manual process and is painful.



> 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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