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I installed Sonoma earlier today.  First time I logged in to my 2019 MacBook Pro Intel 15 inch after the upgrade, I got a notification that an encrypted disk had an unencrypted backup destination.

I have never asked for nor wanted an encrypted disk, and FileVault is still turned off.  All of our iPhone/iPad backups are unencrypted.  (Not only do the sync windows say so, I have manually copied readable MP3s and JPGs from the backups.)

I have never created a password or encryption key for such because I have never been asked for one.  Nothing in diskutil list suggests encryption.  Nor in Disk Utility.

If there really is an encrypted disk somewhere, how do I find it and how do I unencrypt it? 

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    What hardware do you have? On most new Macs, the disks are always encrypted whether you want to or not.
    – bmike ♦
    Commented Sep 28, 2023 at 1:52
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    That would suck. I have a 2019 MacBook Pro Intel 15 inch. There's only one disk to be backed up, although there';s a virtual DMG for the watch emulator. Disk Utility says neither is encrypted.
    – WGroleau
    Commented Sep 28, 2023 at 4:04
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    Why is this a problem?
    – benwiggy
    Commented Sep 28, 2023 at 8:40
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    I'll have to investigate whether the change is a new feature of Sonoma. The never-before warning is a bit disconcerting.
    – WGroleau
    Commented Sep 28, 2023 at 14:14

3 Answers 3

Reset to default
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You can confirm whether your disk is encrypted in Disk Utility. In the sidebar, select the Data volume - it may be called Macintosh HD - Data or just Data and review whether it says APFS or APFS (Encrypted)

Based on your post, you've already done this. However I'm answering here with screenshots to confirm where it shows up.

Unencrypted Volume:

Unencrypted Volume

Encrypted Volume:

Encrypted Volume

One thing to note is that encryption is invisible. On Mac laptops, FileVault is enabled by default - but it has no impact on using the system. Except for the encrypted indicator in Disk Utility, etc. everything will operate the same. So - if you did find it was encrypted - that would be the reason why.

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    Correct: FileVault is still OFF, and neither diskutil nor Disk Utility shows any sign of encryption. So the question remains.
    – WGroleau
    Commented Sep 28, 2023 at 1:42
  • And the same notice appeared again when I plugged in the TM drives this morning.
    – WGroleau
    Commented Oct 18, 2023 at 21:03
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If you have an Intel Mac with a T2 chip, or an M-series Apple Silicon Mac:

Data on the built-in, solid-state drive (SSD) is encrypted using a hardware-accelerated AES engine built into the chip. This encryption is performed with 256-bit keys tied to a unique identifier within the chip.

This happens whether or not you enable FileVault during the setup process.

However, the contents of the SSD can still be accessed by anyone who has physical access to the Mac, such as using Target Mode, with no knowledge of the passkey.

So if you are concerned about being able to recover your data in the event of forgetting your password, don't worry: anyone can read it, unless you enable FileVault, which is a separate level of encryption.

The only real benefit of the on-board encryption is that you can just delete the keys, and the disk cannot be read; and if someone tried to unsolder the SSD chips and get them working on another board, your data would also not be read.

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    If a hypothetical snoop has access to "unsolder the SSD chips," then he/she might as well just take the whole laptop and use Terminal in the recovery partition to copy the SSD contents elsewhere. So transparent encryption doesn't really accomplish anything, and FileVault is still needed by anyone who has sensitive data.
    – WGroleau
    Commented Sep 28, 2023 at 14:21
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    @WGroleau Indeed. The only real virtue of it is to effectively 'erase' the disk by deleting the keys in the secure enclave. Though there could be others I'm unaware of.
    – benwiggy
    Commented Sep 28, 2023 at 14:35
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    @VioletGiraffe That's why you have backups.
    – benwiggy
    Commented Sep 28, 2023 at 20:44
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    @benwiggy The other advantage is that if you want to turn on FileVault later, it's pretty much instantaneous. The system simply encrypts the main disk-encryption key with the password you choose (instead of storing it unencrypted so the system can boot unattended). It doesn't have to spend hours and hours encrypting everything that's already on disk. This also avoids putting a bunch of extra wear cycles on the SSD.
    – nobody
    Commented Sep 29, 2023 at 1:31
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    The fact is all SSDs have to scramble the data anyway. This is to prevent certain undesirable patterns from occurring. By replacing the scrambling function by a cryptographically sound one (AES) and plumbing in key management, you get full-disk encryption for nearly "free".
    – user71659
    Commented Sep 29, 2023 at 3:48
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I encountered the same problem, my HD was not encrypted before upgrading to Sonoma and nor was it after the upgrade but the warning poped up immediately. I decided to 'eject' the Time Machine external disk, unplug the cable, and then remount it. Problem solved.

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  • I got the same notification this morning. Whether due to plugging in the drives or to backup trying to start, I cannot tell.
    – WGroleau
    Commented Oct 18, 2023 at 21:02

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