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https://issues.apache.org/jira/browse/HDFS-528?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12739647#action_12739647
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dhruba borthakur commented on HDFS-528:
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It would be nice if we can integrate it along with the safemode code in the NN. 
 Then, no new command line utilities are needed. 

if one set a non-zero value of the new config parameter, then the NN will not 
exit safemode unless that many DNs have checked in. 

> Add dfsadmin -waitDatanodes feature to block until DNs have reported
> --------------------------------------------------------------------
>
>                 Key: HDFS-528
>                 URL: https://issues.apache.org/jira/browse/HDFS-528
>             Project: Hadoop HDFS
>          Issue Type: New Feature
>          Components: scripts
>    Affects Versions: 0.21.0
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>         Attachments: hdfs-528.txt
>
>
> When starting up a fresh cluster programatically, users often want to wait 
> until DFS is "writable" before continuing in a script. "dfsadmin -safemode 
> wait" doesn't quite work for this on a completely fresh cluster, since when 
> there are 0 blocks on the system, 100% of them are accounted for before any 
> DNs have reported.
> This JIRA is to add a command which waits until a certain number of DNs have 
> reported as alive to the NN.

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