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https://issues.apache.org/jira/browse/HDFS-839?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12800970#action_12800970
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dhruba borthakur commented on HDFS-839:
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> what's the rationale for doing so?
I am thinking that the namenode has to spend considerable horsepower to keep
forwarding block reports and blocksReceived to BackupNode. I would like to have
a HA solution without impacting the performance of the NN. Thus, the proposal
to make datanodes send blocks reports and blocks received to NN as well as BN.
> the backup node can just re-replicate any blocks it thinks are
> under-replicated when it becomes the primary.
Precisely.
However, when we fail over from NN to BN, there could be blocks in the BN that
we should quickly find if there are any blocks in the BN that do not have any
valid replicas and then query all datanodes to send a block report for those
blocks.
> 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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