I take backups pretty seriously. It’s the primary reason I switched to Mac: once I learned that I could boot from an external backup drive I wanted that security. Today, when my shiny new external USB 3.0 drives arrived in the mail, I immediately started a backup, but was shocked when I couldn’t boot from the backup! Well… somewhat. I eventually got there, and it wasn’t obvious to me, so I wanted to make sure that you knew what to do.

The Symptom

I did this:

  1. Power down my MacBook Air.
  2. Connect the external drive to the MacBook Air by USB.
  3. Hold down the Alt/Option key while pressing the Power button to turn the computer on.
  4. Wait for the boot menu to appear and list both my internal storage and the external drive as bootable disks.

I waited and waited and waited, but the external drive never appeared in the boot menu, so I couldn’t boot from it.

The Fix

While in the boot menu, disconnect the drive from the MacBook Air, wait a few seconds, then reconnect it. The drive should start to spin and after a few seconds, it should appear in the boot menu. Now you can boot.

Some Details

I booted successfully from the external drive using the Startup Disk section of System Preferences, so I guessed that SuperDuper! had correctly made the backup bootable.

Of course, if I have to first boot from my internal storage in order to subsequently boot from the external drive, then that defeats the purpose of a bootable backup. I need to boot from the external drive precisely when my internal storage fails. (I did this once with my trusty Powerbook G4, whose internal hard disk died. I plugged in my external drive, rebooted, and kept working. Sure, the machine was slow, but it worked for the few days I needed before I could get to a repair shop. Can Windows do this yet?)

I noticed that, at the boot menu, the computer was clearly sending enough power to the external drive, but that the activity light was not flashing with disk activity. With nothing left to lose, my wife disconnected the drive and reconnected it. Suddenly the disk activity light started flashing and, within a few second, the drive appeared in the boot menu. Success!

Just another little stupid trick one needs to have up one’s sleeve to deal with modern technology.