How to correctly delete or purge Time Machine backups under the current macOS 26.2 "Tahoe?

markfromlandolakes wrote:

Note: Earlier threads on this subject mention a "gear icon" I have yet to find any "gear icon". In addition, those threads do not seem to be very accurate or specific.

Is there anyway to delete or purge old "Time Machine" backups? Further, I have not used Time Machine in awhile; I have just setup a new M4 Mac mini and I need to be on top of my Time Machine backups. (Although I have not ever lost any data on any Mac I have owned. I have had to manually move files though unable to use Migration Assistant because I could not login to the old Mac after M1 and M2 Mac mini failures.)

I will have at least two Time Machine Hard drives at any time.

Do old backups get deleted automatically as the drives fill up? If they do, is there any control over this behavior?

I have an M4-4TB Mac Mini and a 4TB SSD Thunderbolt 3 Backup Drive. I don't have even have 1.5 TB of Data used at this time.

I see no way to control the Time Machine process as to managing the storage on the backup device. There seems to be a lack of options or any proper management. If what is going on in the background is appropriate, I have nothing to worry about, but I have no way of knowing what is going on. Each backup file on the Time Machine drive seems to depend on the Previous Files, so deleting an earlier file seems like it would compromise the entire Backup.

I think proper management, (in the background automatically or manually), would be to delete old backups as opposed to simply stopping backups.

If I find no information about a way to delete previous backups, automatically or manually, while maintaining the integrity of the Backup, I will wipe an entire Time Machine backup periodically.

Time Machine backups do regularly "purge" themselves by deleting the oldest backups. However, to be efficient, Time Machine backups share files or pieces of files and connect them via special links that enable a complete recovery for a range of dates, say n dates, while using up a fraction of n x (size of your system). This works because most incremental backups only copy a small fraction of the accounts and system files, e.g. just those that were changed since the last backup.

However in some instances, it is not possible to delete enough files to make room for a new backup because those files are linked to many other backups. When this happens, Time Machine informs the user that the drive must either be erased and backups restarted, or a new backup must be obtained and started.

It isn't possible for the user to manually delete older backups, much for the reasons outlined above. In so doing, pieces of other backup sets would also be deleted and then the backups would no longer work.

Time machine is designed to be controlled by itself. You never want to manually start deleting backup files as it could corrupt the system. TM will auto delete old backups as space is needed. It is recommended to leave the backup drive alone or erase and start a new backup or get another drive as a backup and store the old drive just in case. There may be under certain conditions when TM does not erase the old backups in which case erase and start over is required.

Here is how it works, there absolutely is active management and oldest backups are indeed deleted:

• You can recover files from local snapshots even if your Time Machine backup disk is not available.
• Hourly backups for the past 24 hours
• Daily backups for the past month
• Weekly backups for all previous months
• As the disk gets full, oldest backups are removed to make space

From one of my Macs in the image above: I am using a 2 TB external drive to back up a Mac with an internal 1 TB drive. That backup drive is actually smaller than recommended, I think 4-6 TB would be better, but the drive being backed up is using about 0.5 TB so I have a backup drive about 4x the size of the file space being backed up. The backup drive still has 331 GB available. Its oldest backup is from May 2022. I have other backups drives in use, about 8 or so for multiple Macs, none has ever filled up, all have been used for years.

I have used this Time Machine backup to restore individual files as well as migrate an entire Mac from an older computer that had failed (it was a 2008 iMac). Time Machine has always been self managing, I never have to worry about it.

I also have a SuperDuper clone backup of this Mac. That is to mitigate any risk that something goes wrong with the Time Machine backup or that the TM drive fails.

In addition, I store important files in the cloud off site. That includes Dropbox storage as well as all Messages and my Photos system library in iCloud.

Time Machine has worked well for me for more than 20 years. I have used it to recover accidentally deleted, damaged or lost files, and have used it to "migrate" entire Macs when new ones were acquired. I have done about 20 of these "migrations," all without a hitch, for personal and work Macs, the most recent for my daughter's business, she just got a new M4 Max Macbook Pro and I migrated everything to it from her 2019 Macbook Pro (Intel, 16"). As an aside, those Migrations can also be done using one of those "clone" type backups, such as produced by SuperDuper or Carbon Copy Cloner.

Those of us who find Time Machine useful will continue using it. Those who for whatever reason do not want to use it have many other options, some of which I listed above. For a versioned type backup that requires no user involvement, it's pretty hard to beat Time Machine, however, especially given its user interface and price (free). That said, the best way to reduce risk is to utilize multiple backups including different types of backups stored in different places.

markfromlandolakes wrote:

I’ve just set up this new computer. I just know in the past when I used Time Machine, It would get filled up and backups would cease. Maybe Time Machine works better now, I don’t know.

Nothing functional about Time Machine has changed. You have a problem that I have seen reported here. I (and some others here) do not have that problem.

I started this thread to understand how this works. I’m not looking for anything but actual information.

All of that is on the Apple Support articles. You turn it on and it works. For you it doesn’t, so we are trying to help you figure out why not. There is no hidden settings. There is no way to micromanage it. You turn it on and leave it alone, unless you have some problem like yours. Knowing how it works is not going to solve your problem because there isn’t a problem with how it works to delete old backups. You have a problem where it writes too much data such that the algorithm doesn’t work.

It’s a secret how Time Machine works and how it deletes older backups, that’s unacceptable.

Then use something else.

It says it deletes older backups, the question is, how does this happen while assuring the integrity of the current backup? No one knows for sure.

It deleted what it can delete. As others have noted, there is some magical point at which it can no longer do that, so it doesn’t.

Time Machine is not an archival backup solution. You should only ever believe there is a backup of everything that is currently on your Mac. You should not expect to restore deleted items forever. They should remain as long as there is room, but that time is not defined anywhere. Data is not now nor has ever been duplicated in a Time Machine backup. All subsequent backups just create a file system reference back to the original file. If the file is changed, new storage is written and referenced in future backups. The only thing that can be deleted are original files when a new changed version is written. There is usually no redundant information.

Any Time Machine articles that you find more than a few years old are wrong. The general concepts should be current, but the APFS snapshot scheme alters the underlying “how it works” significantly. From a user perspective, the biggest difference is the lack of delete capability.

You may be able to use the command line tmutil to remove snapshots, but I have no idea what that would do to the backup structure. I also have no idea how you would know what you are deleting as the references appear to be actual files. There is no way to determine if the reference is the only reference. If it is not the only reference, no data will be destroyed until the final reference is deleted.

If you can’t hit the “I believe” button and leave it alone, you should use a different backup system.

Apple has not officially documented its Time Machine file structure. So various people have tried in the past to discern how it works, with some success. Some of these links date from several years ago so TM may have changed some since they were written:

https://tommyang.github.io/pondini.org/TM/Works1.html#:~:text=A%20Time%20Machine%20backup%20folder%20structure%20consists,the%20entire%20file/folder%20structure%20of%20the%20original

https://eclecticlight.co/2021/03/22/time-machine-to-apfs-backup-structure-and-access/#:~:text=Backup%20snapshots%20themselves%20contain%20the,are%20summarised%20in%20the%20diagram.

My understanding, which I admit is likely not perfect, has been gleaned from reading online articles and in particular from discussions I had with a technician in an Apple Authorized Service Provider store, which is a third party shop certified to sell and repair Apple products. He explained that when the oldest backup is removed from a Time Machine set, some of its files may still remain and the hard links that TM uses to recreate a Mac's entire set of files from a specified date are reconfigured and rearranged. While the user sees a nicely ordered and dated set of backups, in fact those often contains scores of links to the physical files. Sometimes TM spends lots of time "cleaning up" after a backup finishes, which is this complex housekeeping, especially when older backups are removed. A backup being removed does not necessarily mean that all the files are being removed from that date, but the ability to recreate the Mac on that date is removed. He also told me that because of this complex structure, deleting individual items on a Time Machine drive using Finder (or Terminal) will result in some or many of the other backups being unusable, as their links to those physical files are broken.

Note that "cloning" Time Machine backup drives does not work anymore, as noted by both the SuperDUper and Carbon Copy Cloner companies. Some have tried even bit for bit copies or clones or other Terminal/Unix tools but from what I have read, none of these work reliably. The links seem to be hardware specific.

Some of this has been gleaned from reports from other users. Some deleted specific backups from their Time Machine drives and found none of their Time Machine backups worked anymore. Others tried to "clone" backups and failed. You can certainly experiment with this yourself. Maybe leave your current Time Machine alone and continue using it normally, but also create a new one that, after it has done several weeks worth of TM backups, can be used for "experiments." It's hard now; Apple makes the TM drive read-only to all users, to prevent damage to the TM backup set, so there's not much you can do now.

markfromlandolakes wrote:

Is there official information from Apple to back up, (no pun), what you are saying. The oldest backup seems to be the largest. These backups would need to be merged in the background making the oldest backup always the base. I see no evidence anything like this is happening.

That’s because that’s not what happens. The initial backup is a backup of everything on your Mac, well all of your data unless excluded. The backup is created by making an APFS snapshot and copying that to your backup drive. After the initial full back up, all changes are constantly monitored by the file system, and that database is used to create an incremental backup of things that are new or changed that snapshot is then synchronized with the original to write the differences to the backup drive. No data is merged, but every backup snapshot will appear to be everything on the drive because that’s how snapshots work. The snapshot is just a bunch of references to the storage location on the drive, it is not copies of the data itself. Does Apple have any documentation of this? I don’t know, possibly.

If you’re looking for documentation to that says you cannot delete a backup, that definitely does not exist. What did exist prior to the APFS backup scheme was an Apple article describing how to delete files or whole backups. That article was disappeared when they introduced the APFS back up scheme and all of the commands to delete something from the backup were removed from the UI.

I should add (see Barney's post about this) that one situation not well suited to Time Machine is use of very large individual files that get changed frequently. An example is a virtual machine, where the entire virtual machine file (which can be many tens of GB in size) will show as "modified" even if all one does is log into the virtual machine and log out. Time Machine will then dutifully back up the entire thing because it was "modified," over and over. This can use up a lot of space on the backup drive. There are several solutions to that situation. One is to reduce the frequency of hourly backups, say to daily. What makes more sense is to exclude those large files (such as VM files) from Time Machine's backups and instead manually back them up using Finder or a clone program to a separate drive periodically. Then Time Machine will run efficiently as designed and you still have backups of those single large files.

Do like Time Machine Backups

Use Carbon Copy Cloner either manually or on a schedule

How to schedule a backup

https://support.bombich.com/hc/en-us/articles/20686449773847-How-to-schedule-a-backup

CCC SafetyNet: Temporary protection for destination content

https://support.bombich.com/hc/en-us/articles/20686475366935-CCC-SafetyNet-Temporary-protection-for-destination-content

I use it daily and CCC , if configure properly, will Purge Older Backup Snapshot

markfromlandolakes wrote:

I just want to know how it works. There is no active management. Every backup drive eventually will get too full and have to be deleted and start over. Old backups are never automatically deleted.

No, there isn't. If you've got a new M4 and haven't used TM for a long period the best way to start afresh is to erase and reformat the drive APFS w/GIUD partition and start anew. That's what I did with my new M4 Mini.

BINGO 👍

It is wise to have multiple backups on multiple external drives.

I recommend using CarbonCopyCloner or SuperDuper in conjunction with or in-leu of Time Machine.

https://bombich.com/ or https://www.shirt-pocket.com/

Knowing how Time Machine backup works is only half the picture.

Have you deleted things off your Mac that you may want to restore later?

If the answer is, Yes, then you may need to enable more space on your backup device or get a bigger backup device if you’re running out of TM space. See the Mac User Guide on Time Machine for more details on these options.

If the answer is, No, then you could erase or delete your Time Machine backup files and start a new Time Machine backup.

Does that help?

John

I have a backup drive twice the size of my internal and have never needed to purge old backups and never needed to erase it and start over. Perhaps I do not create and delete files as much as you.

There is now no way to delete backups.

But, you should have more than one backup, regardless.

markfromlandolakes wrote:

Is there official information from Apple to back up, (no pun), what you are saying. The oldest backup seems to be the largest. These backups would need to be merged in the background making the oldest backup always the base. I see no evidence anything like this is happening.

Refer to the 2 below links

About Time Machine local snapshots

How often local snapshots are saved