Time Machine Backups No Longer Accessible After Clean & Install of OS Sonoma

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Level 1

11 points

Time Machine Backups No Longer Accessible After Clean & Install of OS Sonoma

I have an iMac 2019, 5K, 27 inch

In October 2024 a local technician where I live, west coast Mexico, did a physical cleaning of the iMac which was very dirty after 4 years of use in a very dusty place, then an Erase and Install of OS Sonoma (previously it was Ventura). He did not download the OS through the internet - he put a copy on from his external drive.

I no longer can access the data in my Time Machine backups prior to the installation. The data is there when I select a particular backup and use the Get Info command, but in Finder all I see are the No Entry icons on the various folders which show as containing Zero KB.

Relevant Info: The internal drive of this iMac used to be named 'Macintosh HD' and the data storage volume as seen in Time Machine was called 'Macintosh HD-Data'. Now the iMac drive has been named 'macOS', and the volume for data inside Time Machine is 'macOS-Data'.

To date, I have not been able to discover if the name 'came with' the installation of OS Sonoma, ie is an Apple-sourced change, or if the name was created by the technician.

Questions:

Is this change of name the reason I cannot view data stored in my Backups prior to installation?

If I change the name back to what it used to be, will I solve this issue? I see that I can do this in Finder.

Would changing the name, however, cause any other issues of concern for normal operation?

I am too nervous to make changes without feeling confidence of not causing yet more problems. This Time Machine issue is not the only problem with the iMac since it was serviced by this local tech, who is not Apple trained although he uses the Apple logo in his company docs and website which is why I took a chance on him.

Very grateful for any help that solves this issue.

iMac 27″, macOS 14.7

Posted on Jan 10, 2025 6:50 AM

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Answer 1

John Galt

Level 10

148,086 points

Jan 10, 2025 1:30 PM in response to lifewebb

Yes.
I don't know, but I don't think it will make matters worse.
The technician didn't do you any favors by changing the default name of the startup device, nor by performing an "erase and install". That is seldom justified, if ever. Upgrading macOS is straightforward, does not change the name of the startup device, and your Time Machine backups would not have been affected at all. At this point I don't know if they can be recovered.

Using the Apple logo without authorization is asking for a lot of trouble: Legal - Copyright and Trademark Guidelines - Apple. Installing any version of macOS by any means other than through Apple's internal servers is also asking for trouble.

Lots of sketchy stuff is going on here.

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Answer 2

John Galt

Level 10

148,086 points

Jan 18, 2025 11:58 AM in response to lifewebb

Seems to me you summarized the situation perfectly. To be clear though it should not be necessary to erase the Mac. The most you may have to do is erase the backup drive and start a new set of backups on it. That's the reason you should get an additional backup drive first — you never want to erase your only backup drive.

Time Machine will eventually complain that it can't find the "original" backup because you erased it. No problem, just remove that one from the list.

Time Machine also tries to accommodate unexpected renaming of Macs and their startup disks, and it's very conservative in that regard. It will assign internal names for separate backups of identically named Macs (for example) and keeps track of them. And, if someone changes the startup disk from its default "Macintosh HD" name it will keep track of that too. Perhaps that's the reason the backups bear the original "macOS" name. Or, as the second tech speculated, perhaps the first tech renamed the Mac to something else.

In any event you can clear up all that potential for confusion by assigning the name of your Mac in Sharing to a name that makes sense to you: Change your computer’s name or local hostname on Mac - Apple Support.

Along that same line of thought is that Time Machine may consider that a renamed Mac a completely new one, and will start a completely new set of backups for it. That's the "conservative" aspect I alluded to earlier — when in doubt TM will never alter or erase backups of what might be a different Mac.

If that should occur the capacity of the backup drive may appear to have been inexplicably reduced, and all of a sudden TM will say it can't back up because the backup drive is full. That causes all sorts of confusion and subsequent trouble when a user attempts to drag TM backup items to the Trash in a misguided effort to reclaim space (don't do that). Again, the solution is to erase the backup drive, start a new set, and never leave yourself without an additional backup that you are sure is complete and intact. It doesn't take too much more logical reasoning to conclude you really ought to have a minimum of three.

I disagree it would take monumental effort to restore individual items from the old backups, even if Time Machine considers them backups of a "different" Mac. To do that hold an Option key while selecting the Time Machine icon in the Mac's menu bar, and select "Browser Other Backup Disks..."

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Answer 3

lifewebb Author

Level 1

11 points

Jan 18, 2025 8:53 AM in response to John Galt

John Galt wrote:

Once you rename the startup disk Time Machine may start a new set of backups, because changing a computer's name will cause TM to "think" it's backing up a completely different Mac. I believe that will also hold true for renaming the volume it's backing up, which would normally be named "Macintosh HD - Data" but I am not certain of that.

First of all, I want to belatedly thank you for taking the time to write everything in your whole response. I have been buried in my main trouble, which is an as yet undiagnosed cause of crashes and restarts which started about a month after the iMac was "serviced" by the technician.

I used to have two backup drives but one of them got erased when I was thinking of replacing it, selling it. It's not an SSD, is about 6 years old but without any other use than backups, and now I think I will bring it back into service until I can afford to buy a new 2nd TM backup drive. So thanks for reminding me!

Re. your quoted words above: I can tell you that although I have changed the name of the HDD to be what it was - Macintosh HD with a volume called Macintosh HD - Data - and have done some backups since making the change, Time Machine regards this computer as still being called macOS. The naming by the tech when he erased the drive appears permanent until I do a new erase and install myself. I believe he did the erasing and installation naming himself or 'macOS' as the User then removed himself and put me in as the User just before bringing the machine back to me.

Another local technician has looked at this situation and says that Time Machine regards the backups dated prior to work done by the technician as one computer, and it regards the backups since the change of HD name at the time of erasure and installation of Sonoma as a different computer. He said it could be possible to restore data from the old backups but it would be very labour intensive, even for just one backup. I certainly know that the iMac currently does not regard me as having permission to access the data on the old backups. What a mess, never predicted or advised to me before actions were taken!

I now think that he did not use my iMac to erase the drive. It was done in one of his computers. Maybe that computer was called macOS. Certainly the Users folder was modified on the day he brought the iMac back to me.

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Answer 4

lifewebb Author

Level 1

11 points

Jan 10, 2025 2:17 PM in response to John Galt

Thank you so much John Galt.

I guess if Finder allows change of name of the HD then by extension it would allow me to change it back again. So I may take that risk but do wonder how the new 'address' would affect my 269 of GB data currently on the computer. Some of it dates to the Macintosh HD era, a lot dates to this macOS era since end of October last year.

The reason the Fusion drive was erased is because the computer was playing up a lot and had become impossibly slow. Maybe there was corruption to get rid of. He did try to do a normal installation from Apple in my house but it would have taken too many hours or not worked at all. So he took it away to his office to open up and do a maintenance cleaning - discovering that it was very dirty due to conditions here. Then he proceeded to erase.

From the time that he checked the drive using a software called CrystalDiskInfo, which said the drive was in good condition but showed many hours of Power On which he thought was a problem, he began to say the Fusion Drive needs replacing with an SSD. Wouldn't cost much... But I am always on a tight budget so I declined.

There is a system in place here in Mexico to obtain recourse for sale of poor quality services or products. I may need to use that system of complaint as this Time Machine backup issue has taken up quite a lot of time. There are several other issues taking up much time as well. Will be posting separately about the most disturbing of those.

Again many thanks for responding John, I feel a bit better already! Thanks for the link to use of Apple's logo as well.

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Answer 5

John Galt

Level 10

148,086 points

Jan 10, 2025 5:50 PM in response to lifewebb

I think the first order of business would be to obtain a second backup drive and use it to augment the first one. Why? One and only one backup drive doesn't comprise a robust backup strategy anyway. If you're serious about backups (which you are, otherwise you would not be concerned) you should have at least two. Any drive can fail at any time, including backup drives, and that isn't even related to the problem at hand.

I don't believe you will be risking anything if you were to rename the startup disk "Macintosh HD". Curiously, Apple has stuck with that name for decades, but why fix what isn't broken. As far as I know it is the only place you will see them use the original name Macintosh. Everything else has become Mac, macOS, etc.

Once you rename the startup disk Time Machine may start a new set of backups, because changing a computer's name will cause TM to "think" it's backing up a completely different Mac. I believe that will also hold true for renaming the volume it's backing up, which would normally be named "Macintosh HD - Data" but I am not certain of that.

Your existing backups are almost certainly intact and restorable, and you can probably access them by holding an Option key while selecting the TM icon in the Mac's menu bar. A previously unseen "Browse Other Backup Disks..." option will appear. Try that.

Then, go ahead and buy another backup drive, rename the startup disk (if you so choose), and initiate that redundant set of backups. TM will back up to both of them "in rotation" whenever one or the other is available.

So that you don't wind up with at least two separate and distinct sets of backups on both disks, you may eventually elect to erase the first backup disk and start a new set. After some time (weeks, months, it's up to you), erase the other one and start a new set on it. Repeat every few months or years, whatever suits your needs.

Personally I wouldn't spend too much time or effort going after that local tech. Lesson learned, no harm done, but they're only putting themselves at risk.

The reason the Fusion drive was erased is because the computer was playing up a lot and had become impossibly slow. Maybe there was corruption to get rid of.

Maybe, and erasing it might prove worthwhile for that reason, but I was never very enamored with Fusion Drive to begin with, and replacing the entire startup drive with a SSD may be in your future. Having backups allows you the comfort of time to keep using that Mac with its possibly flaky Fusion Drive until you can no longer tolerate it.

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