I'm not 100% sure I follow; a hard drive/physical host failure is an unrecoverable error for "single node high availability" (since we only store the recovery state on the HDD). If you're referring to the "unofficial" NFS storage, though, then starting a new Master on a different node would kick in app/Worker recovery just as with ZooKeeper mode. The only distinction would be that you must give *new* applications the IP of the new Master (or just assign the new Master the old one's IP address). Preexisting apps should continue to work.