Or both the options are used together. NFS + SNN ?
On Wed, Apr 3, 2013 at 8:10 PM, Rahul Bhattacharjee <rahul.rec....@gmail.com > wrote: > 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 > > >
