Using Tahoe 26.1 on M3 iMac. Time Machine backup fails with message that disk was formerly encrypted but is no longer encrypted. I have not done anything to unencrypt the disk and in fact I don't recall asking for it to be encrypted.
iMac 24″, macOS 26.1
If you're willing to part with the old backups, then starting a fresh TM backup is likely the easiest solution.
neuroanatomist wrote:
It may be that your internal storage has become encrypted,…
Mac with Apple silicon and Intel Mac with Intel and T2 encrypts internal storage by default; automatically.
Enabling FileVault re-selects the password, but does not encrypt or re-encrypt the existing and encrypted data.
See page 121:
https://help.apple.com/pdf/security/en_US/apple-platform-security-guide.pdf
MrHoffman wrote:
neuroanatomist wrote:
It may be that your internal storage has become encrypted,…
Mac with Apple silicon and Intel Mac with Intel and T2 encrypts internal storage by default; automatically.
Enabling FileVault re-selects the password, but does not encrypt or re-encrypt the existing and encrypted data.
See page 121:
https://help.apple.com/pdf/security/en_US/apple-platform-security-guide.pdf
Thank you, yes...I am quite aware. Fair point and I should have stated that the encryption key was changed, as I did subsequently in the same post when I stated that turning off FileVault removes the login password from the encryption key, and I did not state that the data would be decrypted.
I am aware that the data are hardware encrypted, and as Apple states in their documentation, even were someone to remove the SSDs that are soldered onto the logic board and connect them to another device, the hardware encryption would prevent the data from being accessed. That sure sounds secure, doesn't it?
However, I have stopped emphasizing that the data are encrypted without FileVault enabled, after @etresoft explained to me that if FileVault is not enabled, one need only follow the steps provided by Apple to reset the login password and that will allow access to almost all of the data on the internal drive (keychains and any encrypted disk images notwithstanding). So from a practical standpoint, the hardware encryption provided by the T2 chip or Apple Silicon is pretty much irrelevant if one can so easily circumvent it unless FileVault is enabled. I suspect that's why Apple turned it on by default with the Tahoe upgrade.
Many thanks for your replies.
It seems that my external Time Machine disk was encrypted by FileVault automatically during a system upgrade.
The Time Machine error message says that the external disk I use for Time Machine was encrypted and is no longer encrypted so the backup fails.
The external drive is not visible in Disk Utility.
Should I reformat the drive and start over again with Time Machine? Or is there another fix to reset the encryption tag on an external drive?
It may be that your internal storage has become encrypted, Tahoe turned on FileVault by default without user intervention. Check System Settings > Privacy & Security > FileVault.
You can turn it off, that will remove your login password from the encryption key. Leaves your data potentially accessible to others, but if that doesn’t concern you then go for it.
Time Machine backup fails due to encryption change
