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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 Tue, 18 May 2010 07:11:43 GMT

    [ https://issues.apache.org/jira/browse/HDFS-528?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12868553#action_12868553
] 

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

Hi Dhruba,

It seems you agreed with the original premise of the issue, for the reason of avoiding replication
storms early in NN startup. Certainly you can do this with an external tool, force it to always
start in safemode, and manually (through the tool) kicking it out of safemode when you're
ready. But why not let Hadoop do this for us?

The reason of the error message I see as a bonus on top of a feature which is generally useful,
and which I dont think we should force every operator to write when it's so simple to integrate
into the existing feature. FWIW this code has been shipping with CDH for 8 months with no
issues.

> 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: 0.22.0
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>         Attachments: hdfs-528-v2.txt, hdfs-528-v3.txt, hdfs-528.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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