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Hadoop >> mail # user >> RE: NameNode failure and recovery!

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Re: NameNode failure and recovery!
There is a 3rd, most excellent way: Use HDFS's own HA, see

On Wed, Apr 3, 2013 at 8:10 PM, Rahul Bhattacharjee
> Hi all,
> I was reading about Hadoop and got to know that there are two ways to
> protect against the name node failures.
> 1) To write to a nfs mount along with the usual local disk.
>  -or-
> 2) Use secondary name node. In case of failure of NN , the SNN can take in
> charge.
> My questions :-
> 1) SNN is always lagging , so when SNN becomes primary in event of a NN
> failure ,  then the edits which have not been merged into the image file
> would be lost , so the system of SNN would not be consistent with the NN
> before its failure.
> 2) Also I have read that other purpose of SNN is to periodically merge the
> edit logs with the image file. In case a setup goes with option #1 (writing
> to NFS, no SNN) , then who does this merging.
> Thanks,
> Rahul

Harsh J