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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 Wed, 18 Nov 2009 20:40:40 GMT

    [ https://issues.apache.org/jira/browse/HDFS-718?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12779654#action_12779654
] 

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

Why are you concerned about making this a "cheap" operation?  

Also, why does the name node need to be up to get this info?   format runs on the machine
that the data is stored:  so you have access to the hostname and the fsimage.. which means
that the message that Todd suggests can be calculated.

Maybe I'm just missing something here.  All I'm really seeing is that someone at Facebook
wasn't paying attention and made a mistake.  It happens. But chances are good that a script
that formats the name node is also going to be putting down a config at the same time.   Perhaps
instead the format script you guys have should be checking the size of the image.

I'm just not buying this is a change that needs to be made, especially compared to other file
system technologies.

> 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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