We do not have Automatic failover in our NAS-R3 (DSS will have this near November this year for the NAS - not sure for NAS-R3). If using Microsoft you can use there clustering feature. If using NFS mounts simply remount to the second NAS share.
If using a bonding I would recommend Balance RR.

Update to Auto Failover!!

Please be advised that Auto-Failover has been delayed - there is no set date or details related to this subject.
We will announce this at a later date. Thank you for your patience on this matter.