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https://issues.apache.org/jira/browse/HDFS-839?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12800212#action_12800212
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dhruba borthakur commented on HDFS-839:
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Hi Wang, thanks for your document. It is very nicely written and easily
understandable. Here the the notes I made myself while reading your document:
1. new transactions from clients are blocked when the primary namenode is
syncing transactions to a new slave
2. The automatic promotion of a slave to be a master (when the original master
dies) based on zookeper is something for the future
3. The datanodes will send block reports only to the master. so when a failover
occurs you have to restart (or somehow tell) the datanodes to start sending
block reports to the new master. This can increase failover times drastically.
4. I think we will somehow have to handle the split brain scenario where there
are two masters running on the same cluster. We have to prevent such a case.
5. Your future section regarding Backupode looks great.
Thanks for the hard work. let's continue our dicussion here.
My thinking is that datanodes would have to send block reports/block received
to all the masters. This reduces the number of masters you can have in your
system. But it will make the failover times quick and fast. any thoughts?
> 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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