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From "Konstantin Shvachko (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-11090) Leave safemode immediately if all blocks have reported in
Date Thu, 10 Nov 2016 05:23:59 GMT

    [ https://issues.apache.org/jira/browse/HDFS-11090?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15653078#comment-15653078
] 

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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