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From "Todd Lipcon (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 15:13:14 GMT

    [ https://issues.apache.org/jira/browse/HDFS-528?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12742401#action_12742401
] 

Todd Lipcon commented on HDFS-528:
----------------------------------

Steve: see Dhruba's comment above. In the case of an entirely empty DFS it makes sense that
the NN should stay in safe mode until at least one DN shows up. This will help with some newbie
errors where the DFS appears to be running but in fact nothing works right because there are
no DNs. It also helps with the issue Dhruba mentioned involving unneeded replication during
startup, and is more principled than just picking a large number for dfs.safemode.extension.

I've got the bug I mentioned last night fixed and will upload a new patch after I do a bit
of "burn in" in our sandbox.

> 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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