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Posted to common-issues@hadoop.apache.org by "Todd Lipcon (Commented) (JIRA)" <ji...@apache.org> on 2012/01/07 00:49:39 UTC

[jira] [Commented] (HADOOP-7961) HA: fencing mechanism

    [ https://issues.apache.org/jira/browse/HADOOP-7961?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13181700#comment-13181700 ] 

Todd Lipcon commented on HADOOP-7961:
-------------------------------------

the delta patch looks good to me.
                
> 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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