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From "Allen Wittenauer (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-718) configuration parameter to prevent accidental formatting of HDFS filesystem
Date Thu, 05 Nov 2009 21:21:32 GMT

    [ https://issues.apache.org/jira/browse/HDFS-718?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12774080#action_12774080
] 

Allen Wittenauer commented on HDFS-718:
---------------------------------------

The HDFS implementation currently matches what mkfs and related tools do: if specify the wrong
slice, it is going to get formatted.  

I think the biggest problem here is really that the startup message is too verbose for an
admin to notice they are on the wrong node.  [If you are running multiple namenodes on the
same node, well... you've got other issues.] I'd much rather see a patch that changes the
startup message.

> configuration parameter to prevent accidental formatting of HDFS filesystem
> ---------------------------------------------------------------------------
>
>                 Key: HDFS-718
>                 URL: https://issues.apache.org/jira/browse/HDFS-718
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: name-node
>    Affects Versions: 0.22.0
>         Environment: Any
>            Reporter: Andrew Ryan
>            Assignee: Andrew Ryan
>            Priority: Minor
>         Attachments: HDFS-718.patch.txt
>
>
> Currently, any time the NameNode is not running, an HDFS filesystem will accept the 'format'
command, and will duly format itself. There are those of us who have multi-PB HDFS filesystems
who are really quite uncomfortable with this behavior. There is "Y/N" confirmation in the
format command, but if the formatter genuinely believes themselves to be doing the right thing,
the filesystem will be formatted.
> This patch adds a configuration parameter to the namenode, dfs.namenode.support.allowformat,
which defaults to "true," the current behavior: always allow formatting if the NameNode is
down or some other process is not holding the namenode lock. But if dfs.namenode.support.allowformat
is set to "false," the NameNode will not allow itself to be formatted until this config parameter
is changed to "true".
> The general idea is that for production HDFS filesystems, the user would format the HDFS
once, then set dfs.namenode.support.allowformat to "false" for all time.
> The attached patch was generated against trunk and +1's on my test machine. We have a
0.20 version that we are using in our cluster as well.

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