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If I have an external hard drive with a bootable cloned backup (via SuperDuper) - if I encrypt it with the Finder will I still be able to boot from it if necessary?

Are there any solutions to enable my backup to be both encrypted and also bootable? I currently use FileVault 2 to encrypt my main SSD, and if I try booting from that (i.e. just booting up my computer) it asks for my password. If I try to boot from a bootable external disk (which happens to be encrypted) will it just ask for the disk password on boot [that is, after I select that as the boot disk], similarly to how I would be asked to enter a password to unlock the SSD encrypted with FileVault 2?

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It should work, but if you use SuperDuper! a workaround is necessary:

I backed up my main system volume (hereinafter referred to as "System") to the unencrypted! backup volume (hereinafter referred to as "SystemBackup"). After rebooting to SystemBackup i tried to encrypt the volume SystemBackup, which wasn't successful, because the Recovery HD on the backup disk is missing. SuperDuper! only creates a copy of the system volume.

  1. To get around this you first have to install a working system on the backup disk or use another way to create a Recovery HD volume on the backup disk and then erase the main backup volume again.
  2. Backup your main system volume to the backup volume.
  3. Boot to your (bootable) backup volume SystemBackup
  4. Enable File Vault 2 in the system preferences.
  5. Reboot to SystemBackup like advised and continue encrypting.
  6. After encryption has finished boot to your main volume again
  7. Now backup your main volume as usual using SuperDuper!

In my second/third attempt i used CarbonCopyCloner. In contrary to SuperDuper! CCC creates a backup, which usually includes the Recovery HD:

  1. Backup your main system volume to the unencrypted! backup volume. You might have to initiate the backup of the Recovery HD manually. In my first attempt it was backed up automatically and in a second attempt i had to initiate it manually.
  2. Boot to your (bootable) backup volume SystemBackup
  3. Enable File Vault 2 in the system preferences.
  4. Reboot to SystemBackup like advised and continue encrypting.
  5. After encryption has finished boot to your main volume again.
  6. Now backup your main volume as usual using CarbonCopyCloner.

Even after completely deleting my main disk (File Vault volume & Recovery HD) to simulate a disk failure, i have been able to boot to my system backup volume.

Don't encrypt the backup volume in the Finder (e.g. control-click on the the volume) before or after backing up your main volume!

An important note from the CCC knowledge base:
Mac firmware cannot "see" FileVault-protected volumes larger than 2.2 TB when the disk is attached via USB. If attaching the disk to your Mac via Firewire or Thunderbolt is not an option, create a 2TB partition at the beginning of the external disk to work around this limitation.

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  • So are you saying that I first need to install OS X on the external SystemBackup, then back up the main System HD? Sorry - your answer was unclear.
    – Jason
    Commented Oct 6, 2015 at 15:09
  • @Jason If you use SuperDuper!, yes! The purpose of the first installation of OS X on the external drive is just the creation of a Recovery HD. I've tested the two methods above (SD! & CCC) in a VM. Since you didn't reply earlier, I've deleted the VM meanwhile. I can't verify it anymore.
    – klanomath
    Commented Oct 6, 2015 at 15:27
  • There may be notes on this process here: peter.upfold.org.uk/blog/2015/05/10/…
    – Paul D. Waite
    Commented Nov 30, 2016 at 20:07
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In my opinion this should work. To play safe: If you are able to create a bootable USB stick with a full blown OS installation, try it. :)

The only thing I am currently thinking about is, when you started from your harddisk and encrypt an external drive, the keys for the drive (if it is bootable) need to be on the drive you are encrypting. Otherwise on boot the keys are looked up, but they are on another drive.

To play around with that I would do as I honestly do not know it exactly:

  • Open DiskUtility and prepare a 32GB USB stick for Mac OS X installation (if necessary).
  • Download the Yosemite installer from AppStore.
  • Install Yosemite onto the USB stick.
  • Either way: encrypt USB stick and try to boot from - OR - boot from USB stick and start encryption there (you need PLENTY of time for that)...

If that works, you do the same procedure with your external harddisk.

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When you encrypt a disk with filevault 2, your mac will start up from the recovery disk to load your OS. At the login screen you enter your password to decrypt the disk. It means that it will take some more time to log you in. I think it will work as log as you have a recovery partition.

But if you do not really need filevault on the external drive, i would suggest not using it due to performance/speed.

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I made a bootable encrypted clone using SuperDuper on OS X 10.11.

All I had to do was to reformat my Samsung External T3 SSD with Disk Utility to be Mac OS Extended (Journaled, Encrypted) like this:

Then I cloned my system drive with SuperDuper from my Macbook Pro onto the external SSD.

That's all I had to do. After that I could boot off the external device and everything was fine. And everything was encrypted by Disk Utility and passwords were prompted for and accepted at the appropriate times.

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