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https://issues.apache.org/jira/browse/HDFS-839?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12800750#action_12800750
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Eli Collins commented on HDFS-839:
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bq. I would rather make the datanode send block reports and block received
messages directly to the master as well as the BackupNode. do you agree?
Once nice thing about having the namenode sync to the backup node is that there
should be less divergence in state (eg the block maps) so you have an easier
coherency problem between the primary and the backup. Can't think of why
divergence would necessarily be hard to deal with though, eg the backup node
can just re-replicate any blocks it thinks are under-replicated when it becomes
the primary.
Also wondering aloud if it would make implementing snapshots easier if the
namenode gets to update the backup node state, eg could do so atomically.
Having the datanodes send block reports/received directly to the backup node
seems like it could work as well, what's the rationale for doing so?
> 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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