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https://issues.apache.org/jira/browse/HADOOP-7961?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13181722#comment-13181722
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Eli Collins commented on HADOOP-7961:
-------------------------------------
Thanks Todd, I've committed this.
> HA: fencing mechanism
> ---------------------
>
> Key: HADOOP-7961
> URL: https://issues.apache.org/jira/browse/HADOOP-7961
> Project: Hadoop Common
> Issue Type: Sub-task
> Components: ha
> Reporter: Todd Lipcon
> Assignee: Todd Lipcon
> Fix For: HA Branch (HDFS-1623)
>
> Attachments: hadoop-7961-delta.txt, hdfs-2179.txt, hdfs-2179.txt,
> hdfs-2179.txt
>
>
> In an HA cluster, when there are two NNs, the invariant that only one NN is
> active at a time has to be preserved in order to prevent "split brain
> syndrome." Thus, when a standby NN is transition to "active" state during a
> failover, it needs to somehow _fence_ the formerly active NN to ensure that
> it can no longer perform edits. This JIRA is to discuss and implement NN
> fencing.
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