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https://issues.apache.org/jira/browse/HDFS-2179?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13069846#comment-13069846
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Eli Collins commented on HDFS-2179:
-----------------------------------
Agree with your proposal, though we shouldn't need to fence the old NN in the
cooperative case (because the old primary has confirmed that it's gone into
standby, closed its storage dirs, stopped service threads, etc). Since we have
to make the uncooperative case work anyway, and exercising it frequently/by
default will help find the relevant bugs (eg place where we're not syncing the
log but should be) we should start with it.
> HA: namenode fencing mechanism
> ------------------------------
>
> Key: HDFS-2179
> URL: https://issues.apache.org/jira/browse/HDFS-2179
> Project: Hadoop HDFS
> Issue Type: Sub-task
> Components: name-node
> Reporter: Todd Lipcon
> Assignee: Todd Lipcon
>
> 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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