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https://issues.apache.org/jira/browse/HDFS-779?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14080148#comment-14080148
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Robert Chansler commented on HDFS-779:
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It's a lot of fun revisiting the past while Allen is on a campaign to clean up
Jira!
That this issue seems to have been ignored for four years seems testimony that
simultaneously losing multiple racks--without taking out the Name Node--is not
a serious problem in practice. Still my intuition says that if you ever got to
a situation where the replication queue is multiple racks long, you are better
off in safe mode than a desperate scramble to do replication that may be doomed.
So, does anyone have a report of losing multiple racks and the system
recovering--or not?
> 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: namenode
> 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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