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Restoring a Time Machine Backup on an Ecrypted Drive in Recovery Mode

Hello


2018 15" Macbook Pro

Mojave 10.14.2


I have done a Time Machine Backup to an external hard drive.


My Macbook Pro is being taken for repair soon and so the internal hard drive may be erased during the repair process and I want the ability to restore to the Macbook from the Time Machine backup on my external hard drive.


I know that to do this, you must enter recovery mode and choose to restore from the Time Machine external drive.


The issue is this: before I created the Time Machine backup on this external drive, I formatted the drive as "Mac OS Extended (Journaled, Encrypted)" and encrypted the drive with a password for security reasons.


This means that any time you plug the drive in, the computer asks you to enter a password to unlock the drive.


NOTE: I don't just mean that I encrypted the Time Machine backups. I mean actually encrypted the drive itself using Disk Utility. I did also encrypt the Time Machine backups however (by selecting "encrypt backups" within Time Machine)


My concern is about how this password encryption might affect the ability to access/restore from the external drive when I am in recovery mode. In recovery mode, I have never seen a Mac system prompt the user to enter a password to access an external drive and I wonder is that because recovery mode does not have the ability to access encrypted drives. If that is the case, then I might not be able to restore from the Time Machine backup on this external drive.


If anyone has experience with this, I would be grateful for your advice


Thanks

MacBook Pro 15″, macOS 10.14

Posted on Jul 26, 2022 2:00 AM

Reply
Question marked as Top-ranking reply

Posted on Jul 27, 2022 3:11 PM

Still only one layer of encryption being applied here. Considering that you formatted the drive as encrypted in Disk Utility, if you unchecked the option for encrypted backups in the Time Machine setup process, macOS would have started decrypting your backup drive immediately (and unless you erase it, that takes a long time to complete).


Regarding Time Machine System Restore, I think the setup flow looks something like this:


  1. You launch the app in macOS Recovery and go past its welcome screen.
  2. Select the backup drive and unlock it if necessary.
  3. On the next screen, select the backup you wish to restore (by startup disk and date).
  4. On the final screen, choose which internal partition to erase and restore the backup contents to. The “Continue” button on this screen is changed to “Restore” I think.


Also, if you were to use the app to roll back to a Time Machine local snapshot, step 4 is skipped (the startup disk or data volume that hosts the snapshot is implied), and a final warning appears instead. Snapshot rollbacks take less than 10 seconds to complete once started, whereas real backup restores can take hours (since external content has to be transferred in).

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4 replies
Question marked as Top-ranking reply

Jul 27, 2022 3:11 PM in response to eoinwalsh

Still only one layer of encryption being applied here. Considering that you formatted the drive as encrypted in Disk Utility, if you unchecked the option for encrypted backups in the Time Machine setup process, macOS would have started decrypting your backup drive immediately (and unless you erase it, that takes a long time to complete).


Regarding Time Machine System Restore, I think the setup flow looks something like this:


  1. You launch the app in macOS Recovery and go past its welcome screen.
  2. Select the backup drive and unlock it if necessary.
  3. On the next screen, select the backup you wish to restore (by startup disk and date).
  4. On the final screen, choose which internal partition to erase and restore the backup contents to. The “Continue” button on this screen is changed to “Restore” I think.


Also, if you were to use the app to roll back to a Time Machine local snapshot, step 4 is skipped (the startup disk or data volume that hosts the snapshot is implied), and a final warning appears instead. Snapshot rollbacks take less than 10 seconds to complete once started, whereas real backup restores can take hours (since external content has to be transferred in).

Jul 27, 2022 7:49 AM in response to eoinwalsh

Hi eoinwalsh,


On an external drive, formatting it as encrypted in Disk Utility and checking the "Encrypted Backups" checkbox both do the same thing. They encrypt the partition that holds the backups. In your case, you're ok - there's only one layer of encryption being applied here.


The Time Machine System Restore app (Restore from Time Machine in macOS Recovery) should be able to unlock an encrypted backup drive with no issues. If you want to test this, follow these steps:


  1. Start up from macOS Recovery: Hold down Command-R as you power on or restart your Intel-based Mac. Release the keys when the Apple logo and a progress bar appears.
  2. When the list of utilities appears, select Restore from Time Machine.
  3. Follow the onscreen instructions until you're prompted to confirm the restore. At that point, you can cancel the process. During the setup phase, you should be prompted to provide the password to unlock your encrypted backups.

Jul 26, 2022 9:27 AM in response to eoinwalsh

In Recovery Mode, Disk Utility is available and can be used to mount drives, including encrypted drives (which will prompt for password). You may need to select > View > Show all Devices in DU to see the connected drive.


Note that in general, double encryption is both unnecessary and undesirable. Not sure why you'd encrypt an external drive, then use TM's encrypt backup option as well. If there's time, you may want to create a fresh backup with only TM encryption.


Personally, for my four in-home Macs in addition to TM backups on a 20 TB NAS, I use a pair of 5 TB external drives to swap out as offsite backups. On those APFS-formatted drives I have five volumes, four that are unencrypted but used for TM backups (with encryption) of the four Macs, and a 5th volume that is encrypted (using DU) for general file storage.

Jul 27, 2022 2:19 PM in response to Encryptor5000

Many thanks for your reply. To be clear, I don't just have the TM backups themselves encrypted. I have set Time Machine to encrypt the backups and I have encrypted the drive using Disk Utility. So doesn't that mean I have two layers of encryption applied, not one? And is that a problem?


I followed your instructions and the Time Machine System Restore app asked me to "unlock" the drive, which I was able to do with my password. I unlocked the drive and then a "continue" option appeared. I didn't continue because I was afraid this would start the restore process. However, I am curious to know if there is another step after "continue" that I am unable to go through due to me encrypting both the drive itself and the backups. If the drive unlocked and the "continue" option appeared, does that mean I'm all good?


Thanks


Restoring a Time Machine Backup on an Ecrypted Drive in Recovery Mode

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