Unable to exclude former Time Machine disks

Eric in Oakland wrote:

The only thing I've found that works is to eject the three old drives, and run the backups manually. This seems like a ridiculously complicated work-around.

Any suggestions? There's got to be a better way!

Mac Mini Apple Silicon, 32 Gb RAM

If you can not add your TM to exclude other TM drives ...keep it simple, put them in some rotation to side step you issue if there is a complication, and compare your results.

I would do what works.

What I can say is TM likes to have its's own dedicated drive , sometime a new machine/ a new macOS causes some issues where yes you need to erase/reformat/initialize the parent drive as new GUID/APFS and start over.

Erase and reformat a storage device in Disk Utility on Mac

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

Exclude files from a Time Machine backup on Mac

To be proactive you can file a bug report or submit your Apple Feedback here: Product Feedback - Apple

The current stable release of Sequoia including bug fixes, security updates is macOS 15.6.1

Keep your Mac up to date - Apple Support

Keep your Mac up to date - Apple Support

It appears not to be deleting the oldest backups to free up space, as it is supposed to do.

At some point, there aren't any older backups to delete. After the first backup, the only additions are changed files and new files. If you delete files off your Mac, those backups become candidates for "older backups."

I don't know for sure, but if it has to make another full backup, then the older full backups should probably be candidates for deletion.

I have two SSD drives devoted to Time Machine, one 1 Tb and one 2 Tb. They had both just been erased with Disk Utility when this started, so their full capacity is was available.

Are you sure of the error message. There are two similar ones. One is when the backup drive is full and it cannot delete anything to make room. The other is a message stating that your Startup drive is full (Macintosh HD usually). Time Machine now has to make a snapshot on the drive being backed up. That might take more space than is available on that drive and you get that message.

There are also three older spinning disk drives that were once used for Time Machine but no longer are. However, they still show the Time Machine logo, and i can't exclude them from backups. I think they are what's filling up my Time Machine SSDs.

Time Machine doesn't back up other Time Machine drives. I don't think it is possible to make it. You will see those drives in the Exclusion list grayed out.

They have files that I want to keep, so I can't just erase them.

The only thing I've found that works is to eject the three old drives, and run the backups manually. This seems like a ridiculously complicated work-around.

That does sound like it thinks they are being backed up. I don't know how that is possible nor can I offer any ideas on how to remove them. There is no way to delete any backups from Time Machine.

Possibly, eject them all, then start a new backup on your new backup drives. Once that is established, mount the old ones and check that they are in the exclusion list.