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From "Andrew Ryan (JIRA)" <j...@apache.org>
Subject [jira] Created: (HDFS-718) configuration parameter to prevent accidental formatting of HDFS filesystem
Date Tue, 20 Oct 2009 22:45:59 GMT
configuration parameter to prevent accidental formatting of HDFS filesystem
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                 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
            Priority: Minor


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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