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.
2) Use secondary name node. In case of failure of NN , the SNN can take in
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.