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Date: Thu, 21 Jan 2010 00:03:19 +0000 (UTC)
From: "Konstantin Shvachko (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Subject: [jira] Commented: (HDFS-839) The NameNode should forward block
 reports to BackupNode
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    [ https://issues.apache.org/jira/browse/HDFS-839?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12803072#action_12803072 ] 

Konstantin Shvachko commented on HDFS-839:
------------------------------------------

I want to backup Dhruba, that passing each and every data-node op through the name-node will substantially increase load on the name-node and that holding lock longer will reduce its productivity. 
Another aspect here is that BN is also a NN. So if you supply it with block locations it will leave safe mode and start play role in block replication/deletion, lease recovery, etc, along with the name-node. If a data-node dies both NN and BN will start replicating its blocks unless you control it. So are we solving the split brain problem here? You can of course forbid replication when NN is in Backup role, but you will have hard time convincing e.g. Allen the solution is bullet proof and bug-free.

> 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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