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Date: Wed, 11 Nov 2009 06:44:27 +0000 (UTC)
From: "Todd Lipcon (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=12776315#action_12776315 ] 

Todd Lipcon commented on HDFS-718:
----------------------------------

I agree with Allen and Rajiv here somewhat.

How about a change to the confirmation message that said something like:

{quote}
*** You are about to format the namenode on foo-cluster.corp.facebook.com ***
This filesystem currently contains 2934823 files and was last formatted on 9/10/09.
To confirm deletion, please enter the number of files contained in this namenode:
{quote}

It's a little bit on the silly side, but would force the operator to be aware of exactly how much data they're deleting. Naturally we should provide a "-y" equivalent that skips the confirmation for use in scripts.

(I suppose the number of files is actually impossible to determine without reading the namespace and replaying the edit log, but the same idea could be done with the hostname - basically anything to get the admin off of "autopilot")

> 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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