First TM Backup on New Mac Mini Not enough space error

That Disk Utility screen shot that I posted, was taken while running Catalina which is also APFS like Big Sur.

According to > https://support.apple.com/guide/mac-help/types-of-disks-you-can-use-with-time-machine-mh15139/mac you do still have a choice.

To prove this point, I just formatted a new Seagate right out of the box.

For what it’s worth, starting with Big Sur APFS is the preferred format for Time Machine backups. Prior to Big Sur HFS+ was the preferred format.

https://support.apple.com/guide/mac-help/types-of-disks-you-can-use-with-time-machine-mh15139/mac

davidvignola wrote:

I formatted the drive and try to do the first backup.

How did you format the External Drive for Time Machine.

It sounds like maybe the external drive did not get reformatted properly.

Open Disk Utility > select the External Drive > select Erase > Name the Drive > select Mac OS Extended (Journaled) for the Format > select GUID Partition Map for the Scheme > Click Erase.

Your only re-formatting the Volume, when you need to re-format to whole Drive.

Open Disk Utility > click on the little View box in the top left corner > select Show All Devices.

Now select the External Drives Main Icon and re-format that as suggested above.

There is no point to format the drive as MacOS Extended (Journaled) because as soon as you select this drive to use with TM the TM reformats it to APFS (Case Sensitive) regardless if you have SSD or HDD. I think they changed drive format for TM in Big Sur.

I am on Mac mini M1 that has Big Sur and as soon I select the drive to be used for Time Machine it reformats it automatic to APFS. Then I deselect the disk to use with Time Machine and reformat it to MacOS Extended (Journaled) and then I go to TM and select this disk to use with TM. Then TM is preparing the drive and after that I see in Disk Utility that is formatted as APFS.

On article you posted to me it says "If the disk is a Mac OS Extended format disk that contains an existing Time Machine backup, you aren’t asked to erase and reformat the disk." so if the disk contains an existing TM backup you cann use it as TM backup but if you select another new disk that has no TM it will reformat it to APFS.

The first image is a drive that I'm already using for Time Machine.

The second image is a new drive just out of the box, that I named TM 2.

Yes depending on the version, Time Machine will ask and/or automatically convert the drive.

At this point, this has nothing to do with the OP's (original poster's) problem, because it sound like the drive it not proper formatted for Time Machine to use or convert.

Big Sur will always format to APFS. It is new with Big Sur as it

is supposedly leveraging the snapshot features of APFS for

backups.

FWIW, I have a M1 MacBook Air since end of November with a 500GB

external SSD and all that time, it has used 380 GB with 190 GB of it

purgeable.

With that said, something is certainly running amok on your system.

Just out of curiosity, do you have other external drives connected?

Unless told not to, Time Machine backs up those as well.

For my purposes, Time Machine is only used for last resort system recovery,

but primarily for incremental app update/upgrade reversal and brain clouds.

All my data is backed up/archived completely separately.

Give this a shot, do the reformat but do not turn on Time Machine.

Then reboot into Safe Mode. While in safe mode start up a first

Time Machine backup while in safe mode and see what happens.

There could very well be some third party app/driver that may be telling Time Machine

things are constantly changing. Also, booting into Safe Mode will also clean out

and "crud" that may be in caches and such.

Needless to say, there is something quite wrong on your system that is causing

Time Machine to go ballistic. Everyones system is unique in someway and if

this was an endemic problem, these pages would be full of the issue. We just need

to find what is not playing nice.

It may also help, if you download Etrecheck from the MacApp Store, run it,

and post the results here. we may spot something or it may uncover something

itself as an issue. (use the "additional text icon at the bottom pf these windows

to post your results.)

Just to add one more possibility, do you have another drive laying around

you can try? For the purpose of this test it doesn't really matter what

kind just so it is large enough. Want to rule out the possibility that it

is not the T5. Also, you didn't say how you were connecting? USB-C

or the regular USB-A? Which ever port you are using try the other.

While the T5 may be good in and of itself, the older controller in it

may possibly not be playing nicely with the new hardware.