Fixing a Broken Time Machine Disk

Written by Fuwn on 2025. 04. 18. (last modified on 2025. 04. 18.)

I don't know how, but the primary Time Machine disk I use for my MacBook Pro became completely broken.

About a month back, I started getting occasional alerts on my Mac letting me know that one of my drives could not be decrypted. I dismissed this message for quite some time as I had changed nothing and noticed no differences in my day-to-day Mac experience. I can't remember for what reason, but at some point I wanted to check out my Time Machine backups or configuration and realised that Time Machine hadn't completed a successful backup in several weeks.

My first thought was to use Disk Utility's First Aid option, which only led to confusion. Below is a copy of First Aid's output.

Erasing “My Passport for Mac” (disk6s2) and creating “My Passport for Mac”

Preparing to erase APFS Volume content
Checking mount state
Erasing APFS Volume disk6s2 by deleting and re-adding
Deleting APFS Volume from its APFS Container
Unmounting disk6s2
Erasing any xART session referenced by XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX
Deleting Volume
An internal error has occurred. : (-69623)

Operation failed…

Something was wrong with the Time Machine disk.

My next step in troubleshooting this issue was to try to repair the drive from a Debian VM. Running `lsblk` did not show the drive, but running `lsusb` did. Running any command to interact with the drive other than `lsusb` didn't register the drive, while `dmesg` showed that the drive was being recognised. I tried GParted just for the sake of it, but of course, it didn't work either. `usbreset` also did not make any difference, not that it should have given any previous indication.

Going back to macOS was next. First, I ran `diskutil unmountDisk /dev/disk6`, then `diskUtil eraseDisk JHFS+ "My Passport for Mac" GPT /dev/disk6`. The output of this command, "You cannot manually format an existing APFS Container disk", gave me a hint as to what my next logical steps should be: deleting the APFS container.

I'll preface that the following is a destructive operation, but as this Time Machine disk is rolling, the data would have been lost regardless, so I decided to proceed.

Using the previous clue, I ran `sudo diskutil apfs deleteContainer /dev/disk6`, successfully erasing the APFS container and restoring the disk to a mostly usable state. However, the disk was not yet 100% ready to be used as a Time Machine disk and required further formatting to appear in the Time Machine menu. Thankfully, this was trivial, and I accomplished it by erasing the disk and formatting it as APFS through Disk Utility. The disk was now ready to use and worked as expected.

I'm unsure why there weren't any existing articles on this issue, or maybe I didn't look hard enough. Either way, if you stumble upon this blog post with a similar issue, I hope you were able to follow my briefly outlined steps and resolve any problems you may have encountered. If you happened upon this post without having gone through any similar headache and read it for the sake of learning, I hope you also found it insightful, or at least entertaining.

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