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Date: Thu, 19 Nov 2009 18:53:39 +0000 (UTC)
From: "Owen O'Malley (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Subject: [jira] Commented: (HDFS-779) Automatic move to safe-mode when
 cluster size drops
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    [ https://issues.apache.org/jira/browse/HDFS-779?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12780198#action_12780198 ] 

Owen O'Malley commented on HDFS-779:
------------------------------------

Other points:
  1. Decommissioned nodes clearly shouldn't count in the totals
  2. The default of 10% DataNode lossage probably makes sense.
  3. The high water mark should be over the last day so that long term gradual losses don't cause problems.

Thoughts?

> 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
>
> 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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