FAQ
DO NOT format your NameNode. Formatting a NameNode is equivalent to
formatting a FS -- you're bound lose it all.

And while messing with NameNode, after bringing it down safely, ALWAYS
take a backup of the existing dfs.name.dir contents and preferably the
SNN checkpoint directory contents too (if you're running it).

The RIGHT way to add new directories to the NameNode's dfs.name.dir is
by comma-separating them in the same value and NOT by adding two
properties - that is not how Hadoop's configuration operates. In your
case, bring NN down and edit conf as:
<property>
<name>dfs.name.dir</name>
<value>/mnt/hadoop/name,/public/hadoop/name</value>
</property>
Create the new directory by copying the existing one. Both must have
the SAME file and structure in them, like mirror copies of one
another. Ensure that this new location, apart from being symmetric in
content, is also symmetric in permissions. NameNode will require WRITE
permissions via its user on all locations configured.

Having configured properly and ensured that both storage directories
mirror one another, launch your NameNode back up again (feel a little
paranoid and do check namenode logs for any issues -- in which case
your backup would be very essential as a requirement for recovery!).

P.s. Hold on for a bit for a possible comment from another user before
getting into action. I've added extra directories this way, but I do
not know if this is "the" genuine way to do so - although it feels
right to me.
On Thu, Feb 10, 2011 at 10:27 PM, mike anderson wrote:
This should be a straightforward question, but better safe than sorry.

I wanted to add a second name node directory (on an NFS as a backup), so now
my hdfs-site.xml contains:

<property>
<name>dfs.name.dir</name>
<value>/mnt/hadoop/name</value>
</property>
<property>
<name>dfs.name.dir</name>
<value>/public/hadoop/name</value>
</property>


When I go to start DFS i'm getting the exception:

org.apache.hadoop.hdfs.server.common.InconsistentFSStateException: Directory
/public/hadoop/name is in an inconsistent state: storage directory does not
exist or is not accessible.


After googling a bit, it seems like I want to do "bin/hadoop namenode
-format"

Is this right? As long as I shut down DFS before issuing the command I
shouldn't lose any data?

Thanks in advance,
Mike


--
Harsh J
www.harshj.com

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postedFeb 10, '11 at 5:18p
activeFeb 10, '11 at 5:56p
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