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Date: Mon, 25 Jul 2011 15:40:11 +0000 (UTC)
From: "Yang Yang (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
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Subject: [jira] [Commented] (HDFS-1623) High Availability Framework for HDFS
 NN
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    [ https://issues.apache.org/jira/browse/HDFS-1623?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13070557#comment-13070557 ] 

Yang Yang commented on HDFS-1623:
---------------------------------

in the design docs, why is "fencing" needed? 
if the namenode uses ZK for leader election, it needs to have a Watcher on the ephemeral node, if the namenode loses its leader status, the Watcher should return "disconnect" or "node removed" event, so that the namenode can naturally shutdown itself. doesn't this achieve what is mentioned in the "fencing" paragraph?

> High Availability Framework for HDFS NN
> ---------------------------------------
>
>                 Key: HDFS-1623
>                 URL: https://issues.apache.org/jira/browse/HDFS-1623
>             Project: Hadoop HDFS
>          Issue Type: New Feature
>            Reporter: Sanjay Radia
>            Assignee: Sanjay Radia
>         Attachments: HDFS-High-Availability.pdf, NameNode HA_v2.pdf, NameNode HA_v2_1.pdf, Namenode HA Framework.pdf
>
>


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