At Yahoo! over the past year we have helped migrate hundreds of our grids? users to YARN. Our YARN clusters have in aggregate run over 18 million jobs with more than 3 billion tasks consuming over 10 thousand years of compute time. With one single cluster running 90 thousand jobs a day. From this experience we would like to share what we have learned about running YARN well, how this is different from running a 1.0 based cluster, and what it takes to migrate your jobs to YARN from 1.0.