If you are not in position to go for HA just keep your checkpoint period shorter to have recent data recoverable from SNN.
and you always have a option hadoop namenode -recover try this on testing cluster and get versed to it. and take backup of image at some solid state storage. ∞ Shashwat Shriparv On Wed, Apr 3, 2013 at 9:56 PM, Harsh J <[email protected]> wrote: > There is a 3rd, most excellent way: Use HDFS's own HA, see > > http://hadoop.apache.org/docs/current/hadoop-yarn/hadoop-yarn-site/HDFSHighAvailabilityWithQJM.html > :) > > On Wed, Apr 3, 2013 at 8:10 PM, Rahul Bhattacharjee > <[email protected]> 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 > > > > > > > > -- > Harsh J >
