Timemachine options. Using same backup drive on new computer.

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Level 1

25 points

Timemachine options. Using same backup drive on new computer.

When trying to set-up Timemachine on a new computer after using the same backup drive on an old Mac computer it presents me with a number of options. I don't want the backup drive to write call the data all over again so how do I get it to only update the new data without losing any of the old data? Also since there are two admissions on the computer does it back up on the data for both admins?

Note to Apple: Please add Timemachine as a topic option

Mac mini (M4)

Posted on Jul 13, 2025 11:31 AM

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Answer 1

den.thed

Level 10

88,756 points

Jul 13, 2025 01:12 PM in response to werdup

After you migrate to the new Mac using the Time Machine backup drive, you’ll want to select Assume Backups.

If you did not migrate from those Time Machine backups, then you will need to start new backups for that Mac.

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Answer 2

werdup Author

Level 1

25 points

Jul 16, 2025 01:20 PM in response to den.thed

Attached is what I see when I open the Time Machine preferences. When you say "Assume Backups" are you referring to 'Claim Existing Backups?' If so, will this only backup anything new since the last backup from the old computer?

BTW The new computer has a different name from the old one. Will the new name show in the in future backups?

If I start a separate backup, does that start at square one and backup the entire disk? I'm not sure if there is room to do that on the backup disk, plus this would take many hours to do I assume.

Thx

[Edited by Moderator]

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Answer 3

rkaufmann87

Level 10

148,032 points

Jul 16, 2025 02:45 PM in response to werdup

External HD's age the same as a computer so if your old Mac's Time Machine External Hard Disk is about 5 years or more old then it would be smart to simply replace it with a new External Hard Disk. If the old External Hard Disk is still working okay then simply repurpose it as additional storage for non-essential data.

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Answer 4

den.thed

Level 10

88,756 points

Jul 16, 2025 02:47 PM in response to werdup

werdup wrote:

Attached is what I see when I open the Time Machine preferences. When you say "Assume Backups" are you referring to 'Claim Existing Backups?

Yes Claim/Assume.

If so, will this only backup anything new since the last backup from the old computer?

Yes it will Claim/Assume the old backups and continue backing up from their.

BTW The new computer has a different name from the old one. Will the new name show in the in future backups?

You should have migrated the User during the initial setup. Now you have two Users a new one and an old one.

If I start a separate backup, does that start at square one and backup the entire disk? I'm not sure if there is room to do that on the backup disk, plus this would take many hours to do I assume.

Yes that starts new backup of the new Mac. Which is going to happen anyway now, because you created a new User.

Thx

You're welcome.

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