Thanks to all of you for precise and complete responses. S o in case of failure we have to bring another backup system up with the fsimage and edit logs from the NFS filer. SNN stays as is for the new NN.
Thanks, Rahul On Wed, Apr 3, 2013 at 8:38 PM, Azuryy Yu <azury...@gmail.com> wrote: > for Hadoopv2, there is HA, so SNN is not necessary. > On Apr 3, 2013 10:41 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 >> >> >>
