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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-839) The NameNode should forward block reports to BackupNode
Date Mon, 18 Jan 2010 08:54:54 GMT

    [ https://issues.apache.org/jira/browse/HDFS-839?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12801701#action_12801701
] 

dhruba borthakur commented on HDFS-839:
---------------------------------------

> t seems like the network overhead of having each DN send it's block report to each backup
node on a large cluster would be higher than a stream from the NN to the backup node

I agree. But since this traffic is going straight from the datanode(s) to the backnode(s),
they will be mostly equally distributed among all the datanodes. The alternative is that the
NN has to streamline all block received messages to the backupnode, this could mean that you
need namenode machines with greater horsepower. If the NN is streaming all blockreceived to
one backupnode, it could still be fine, but if it has to stream it to multiple backup nodes
in parallel that would be quite performance-unsettling. On the other hand, if the namenode
pipelines these blockReceived to a pipeline of backupNodes, then the namenode has to go through
a complex procedure to  handle errors (if any) from the n-th backupnode in the pipleline.


> The NameNode should forward block reports to BackupNode
> -------------------------------------------------------
>
>                 Key: HDFS-839
>                 URL: https://issues.apache.org/jira/browse/HDFS-839
>             Project: Hadoop HDFS
>          Issue Type: New Feature
>          Components: name-node
>            Reporter: dhruba borthakur
>            Assignee: dhruba borthakur
>
> The BackupNode (via HADOOP-4539) receives a stream of transactions from NameNode. However,
the BackupNode does not have block locations of blocks. It would be nice if the NameNode can
forward all block reports (that it receives from DataNodes) to the BackupNode.

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