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From "Steve Loughran (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-528) Add ability for safemode to wait for a minimum number of live datanodes
Date Wed, 12 Aug 2009 13:15:14 GMT

    [ https://issues.apache.org/jira/browse/HDFS-528?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12742339#action_12742339
] 

Steve Loughran commented on HDFS-528:
-------------------------------------

I do something like this in my workflow; block until the the #of workers is above the required
number. for one thing, that number could be >1, for another, 15, for a third 3000. It is
also rought the same action regardless of whether what you are waiting for is the NN or the
JT; its the number of workers a particular bit of the cluster has to help.

Rather than extend safemode, could you have something that just blocks off the NN until its
worker count is above what your specific script wants? After all, it is your script that has
needs, not the NN.

> Add ability for safemode to wait for a minimum number of live datanodes
> -----------------------------------------------------------------------
>
>                 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-v2.txt, hdfs-528-v3.txt, 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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