I have managed to run an MR job in DSE3.0 enterprise edition.
The problem seems to be with reduce job, which is not responding at all.
I suspect it should be because I am using
FileOutputFormat.setOutputPath(job, new Path(args));
to set the output paths, but cassandra (understand it is underlying DFS) is supposedly not responding.
Not sure on how to figure out exact reason for reduce operation hanging.