When NameNode is down, it means that the entire cluster is down. So, the cluster won’t be accessible as it is down. All the services which are running on that cluster will also be down. So, in this scenario, if any user tries to submit a new job will get an error and job will get failed. All the existing jobs which are running will also get failed. So briefly, we can say that when NameNode will get down, all the new, as well as existing jobs, will get failed as all services will be down. The user has to wait for the NameNode to restart and can run a job once the NameNode will get up.