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

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Re: Incompatible namespaceIDs after formatting namenode
For short, here is a script that may be useful for your to remove hdfs
directory on DNs from your headnode.

for each DN hostname
      ssh root@[DN hostname] "rm [your hdfs

On Sun, Jan 15, 2012 at 7:22 AM, Uma Maheswara Rao G

> 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.
> Regards,
> Uma
> ________________________________________
> From: gdan2000 [[EMAIL PROTECTED]]
> Sent: Sunday, January 15, 2012 2:15 PM
> Subject: Incompatible namespaceIDs after formatting namenode
> Hi
> 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
> datanodes...
> Please explain me how all this reformat tasks preserves user's data ?
> --
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