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https://issues.apache.org/jira/browse/HDFS-893?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12800717#action_12800717
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dhruba borthakur commented on HDFS-893:
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another option is to make the datanode(s) send block reports and block received
to both namenode and backupnode. will that work?
> Synchronization other FSNamesystem information to BackupNode
> ------------------------------------------------------------
>
> Key: HDFS-893
> URL: https://issues.apache.org/jira/browse/HDFS-893
> Project: Hadoop HDFS
> Issue Type: New Feature
> Components: name-node
> Reporter: Wang Xu
>
> Backup Node (BN) in trunk brings "warm" standby (HADOOP-4539), it
> synchronizes namespace information from Main NameNode, and leaves DataNode
> information, Block Operation (such as replication), and lease information
> unsynchronized.
> We (team from China Mobile Research Instatitute) had also some experimental
> on Namesystem schronization ( some information has been post at:
> http://gnawux.info/hadoop/2010/01/pratice-of-namenode-cluster-for-hdfs-ha/ ).
> Currently, we are thinking about migrate our code to re-based on Backup Node,
> and we think it might convenience the maintenance of code and contributing
> back to community.
> As NN in current trunk can log all the namespace changes as journals to BN,
> the rest information needed to be synchronized includes:
> - Changes in DataNode Map: information collected from DataNode heartbeats
> and reports. Together with namespace info, the blocks map can also be
> calculated.
> - Lease information: leases are updated by clients periodically or when it
> lock/unlock file for write.
> - Block operation's status, such as pending replication block list: these
> information are depends on random number, thus it may lead to inconsistency
> if do not synchronize them.
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