Re-using old Backup Drive on New Mac

in DU, first, you must be sure to use the "view" menu

and then "show all devices".

before you select the drive at the top level to erase it?

because if you do, you should be given the "format" and "scheme" options.

It is very important the you select the ENTIRE drive, by its immutable manufacturer-given Device name, not any human created name like Macintosh HD.

Use Disk Utility to erase an Intel-based Mac - Apple Support

if you don't see the manufacturer-given device name be sure the little View menu is set to "show all devices"

.

I always feel that it is best to start a fresh backup after upgrading macOS, or moving to a new mac.

if you don't have a need for the old backups, then yes, you may as well erase the drive and start fresh with the new Mac. first remove the drive from TM preferences and then refer to this apple support page to erase the drive >> Erase and reformat a storage device in Disk Utility on Mac - Apple Support

but if you may eventually need those backups, then I would put that drive aside and start fresh with a new drive on the new Mac. and as cheap as external drives have become, why not get a new drive to go with your new Mac?

You can also add an additional drive (or remove an existing drive) at any time.

When you add a drive, Time machine will create a new, stand-alone backup set on the added drive, then alternate drives -- every other backup goes to every-other drive.

As jeffreythefrog says, the 'approved method' for eliminating unwanted Time Machine backups on a drive is to ERASE the drive. Don't try to delete the individual backups.

If you ask Time Machine nicely to remove a backup, it only processes ONE backup (of the dozens remaining on the drive) at a time. They are consolidated, not eliminated, and It takes a very long time for each.

jeffreythefrog wrote:

I could have sworn that I said that in my last reply. I even included screenshots with the entire drive highlighted in the third one. :)

Yes, you did,

And I added similar information, but from a slightly different perspective, to re-enforce what you said.

You started from the detail of selecting "show all devices"

I started from the detail of select the DEVICE by its wonky name, because I see the most common failure as choosing Macintosh HD and thinking you are done.

Then I went on to include the information you did, not to contradict you, but to re-enforce what you said. I also included a link to the official Apple article, which says the same stuff you and I both did in yet another way.

These posts will be here for a long time, and other readers we will never know will find them by searching, but never post anything. I try for the most complete information in the most accessible form, and often that means saying the same stuff a different way.

Please don't read that as criticism. I did not mean to challenge what you said, only re-enforce it.

yes, I get it. and I do understand now that you made your post to help others that may read these forums but not participate. and I can also see that your contribution helped my post, not contradicted it. so again, I'm sorry if you felt that I stepped on your toes. that wasn't my intention.

I could have sworn that I said that in my last reply. I even included screenshots with the entire drive highlighted in the third one. :)

you're welcome. I'm happy you've got it sorted. :)

ok, well thanks for that. and I didn't mean to be snarky. I just thought you didn't see my whole post.