Time Machine Not deleting old backups

I am seeing this problem as well. I have an 8 TB drive backing up a 2 TB MacBookPro. There is 1 TB of empty space, and backups as old as 2021 if I look at the contents. Yet, nothing gets deleted to finish the back up, being told only 75% of the backup could be completed. So two questions:

1). Does this mean it actually kept 75%, or does aborting delete the partial backup?

2). So an 8 TB drive should be plenty large to continue to back up a 2 TB Mac (which is 75% full) , so it seems NO old backups are ever being deleted. And if it only got to 75%, is it trying to backup the entire machine? I would assume it should only backup things that have changed.

Seems TimeMachine may be useless now?

Sounds like a bug to me. Time Machine used to delete old backups to make space for the new one. I saw someone say that old ones are not deleted until it completes the new backup, but that makes no sense at all. If it completed the backup, it did not need to make space.

r2ress wrote:

Time machine is "supposed" to delete older backups to make room for new backups. "Also, as your backup disk fills up, Time Machine deletes older backups to make room for new ones. You may be able to use Time Machine for a long time before running out of space." If the Time Machine backup disk for your Mac is full - Apple Support

I have a 2TB backup drive that is only used for Time Machine to backup a 500GB hard drive which has only 160GB used of which only about 100GB should be backed up based on exclusions. Thus my backup disk is 20 time larger than the files to be backed up. Much more than the 3-4 recommend.

Time machine worked fine for two months (does Apple consider that a "long time"?). Now there are 1.9 TB of backups and time machine stopped a backup with the message:

"Time Machine was only able to complete 8% of the backup because there is insufficient free space on the backup disk."

The backup disk has 50GB of space remaining on it.

I have tried three times to "Back up now" and each time it gives a different percentage and then errors. Here is one example of just before it errors out.

https://discussions.apple.com/content/attachment/3fd4ca7f-6045-456f-8d30-909e81adac1c

Does 249.7 MB at 25% suggest it only needs to back up 1 GB? If so there is 50GB available so what is the issue?

Why is Time Machine not deleting the older backups as the documentation says?

What can be done so Time Machine works as documented?

Start over or get a new backup drive if you want to keep the old Time Machine

Erase and reformat a storage device in Disk Utility on Mac

Erase and reformat a storage device in Disk Utility on Mac - Apple Support

If you value your user data

3-2-1 Backup Strategy: three copies of your data, two different methods, and one offsite.

More than one device, more than one backup methodology.

Do you have any virtual machines you are backing up, or any other monolithic databases?

Do you ever get messages that it must complete another full backup?

when you set up the backup drive, did you set a storage quota for the drive?

Time machine has a mind of its own. Just start a new one as suggested.