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Date: Wed, 18 Nov 2009 19:24:40 +0000 (UTC)
From: "Andrew Ryan (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Subject: [jira] Commented: (HDFS-718) configuration parameter to prevent
 accidental formatting of HDFS filesystem
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    [ https://issues.apache.org/jira/browse/HDFS-718?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12779615#action_12779615 ] 

Andrew Ryan commented on HDFS-718:
----------------------------------

I just attached an updated patch which adds the key to org.apache.hadoop.hdfs.DFSConfigKeys.

@Todd: I'm fine with revising the confirmation message, but at format time the Namenode is down, so there's no easy/cheap way of getting this information about the filesystem that either I or Dhruba know. We're certainly open to suggestions though.

> 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-2.txt, 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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