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Hadoop >> mail # user >> Incompatible namespaceIDs after formatting namenode

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RE: Incompatible namespaceIDs after formatting namenode
Since you already formatted NN, why do you think dataloss if you remove storage directories of DNs here?
Since you formatted the NN, new namespaceID will be generated. When DNs registering to it, they will have still old NamespaceID, so, it will say incompatible namespaceIDs. So, here currently the solution is to remove the storage directories of all DNs.


From: gdan2000 [[EMAIL PROTECTED]]
Sent: Sunday, January 15, 2012 2:15 PM
Subject: Incompatible namespaceIDs after formatting namenode


We just started implemented hadoop on our system for the first time(Cloudera
CDH3u2 )

After reformatting a namenode for a few times, DataNode is not coming up
with error "Incompatible namespaceIDs"

I found a note on this
http://pages.cs.brandeis.edu/~cs147a/lab/hadoop-troubleshooting/ but I'm
really not sure about removing data node directories.

How is it possible that data will not be lost? I have to do it on all

Please explain me how all this reformat tasks preserves user's data ?

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