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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-779) Automatic move to safe-mode when cluster size drops
Date Wed, 15 Sep 2010 05:21:36 GMT

    [ https://issues.apache.org/jira/browse/HDFS-779?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12909598#action_12909598
] 

dhruba borthakur commented on HDFS-779:
---------------------------------------

@Joy: I agree that not losing heartbeats is the best scenario. In the case I mentioned in
my above comment, we would not lose datanode heartbeats if we implement HDFS-1392.

On the other hand, if there is a true network partition, then NN will "lose heartbeats" from
datanodes, because the datanodes cannot send messages to the NN. In that case, the NN should
delay creating a replication-storm in the hope that the network partition gets resolved soon.
So, the heuristic that I listed above to detect a network partition should still be applicable,
isn't it?

> Automatic move to safe-mode when cluster size drops
> ---------------------------------------------------
>
>                 Key: HDFS-779
>                 URL: https://issues.apache.org/jira/browse/HDFS-779
>             Project: Hadoop HDFS
>          Issue Type: New Feature
>          Components: name-node
>            Reporter: Owen O'Malley
>            Assignee: dhruba borthakur
>
> As part of looking at using Kerberos, we want to avoid the case where both the primary
(and optional secondary) KDC go offline causing a replication storm as the DataNodes' service
tickets time out and they lose the ability to connect to the NameNode. However, this is a
specific case of a more general problem of loosing too many nodes too quickly. I think we
should have an option to go into safe mode if the cluster size goes down more than N% in terms
of DataNodes.

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