When the internal drive failed in my late 2012 iMac, I booted into Recovery Mode (command-R) from a USB thumb drive. My Time machine backup was on a Drobo 5D and it didn't appear when connected with a Thunderbolt cable or with a USB 3 cable. It did appear with a USB 2 cable. Is this a limitation of the Drobo 5D, iMac late 2012, or OS X? If I have to restore entire volumes I really want to backup to something that is faster to restore than USB 2.