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https://issues.apache.org/jira/browse/HDFS-11090?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15653078#comment-15653078
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Konstantin Shvachko commented on HDFS-11090:
--------------------------------------------
Hey [~andrew.wang], [~jingzhao] is right - leaving SafeMode immediately after
reaching 100% of minimally (1) replicated blocks will trigger unnecessary
massive block replication. So this would be a big concern for big clusters.
It looks like you are trying to optimize for the very first empty cluster
startup.
One possibility is to add to your management script a startup {{-D}} option,
which sets safemode extension to 0 for the first NN startup. Then you don't
need to update {{hdfs-site.xml}} for subsequent restarts of NN.
> Leave safemode immediately if all blocks have reported in
> ---------------------------------------------------------
>
> Key: HDFS-11090
> URL: https://issues.apache.org/jira/browse/HDFS-11090
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: namenode
> Affects Versions: 2.7.3
> Reporter: Andrew Wang
> Assignee: Yiqun Lin
> Attachments: HDFS-11090.001.patch
>
>
> Startup safemode is triggered by two thresholds: % blocks reported in, and
> min # datanodes. It's extended by an interval (default 30s) until these two
> thresholds are met.
> Safemode extension is helpful when the cluster has data, and the default %
> blocks threshold (0.99) is used. It gives DNs a little extra time to report
> in and thus avoid unnecessary replication work.
> However, we can leave startup safemode early if 100% of blocks have reported
> in.
> Note that operators sometimes change the % blocks threshold to > 1 to never
> automatically leave safemode. We should maintain this behavior.
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