User profile for user: boerstj1
boerstj1 Author
User level: Level 1
4 points

Time machine back ups on 2 macs are different file sizes

I used migration assistant to set up my new MacBook Air 2025 from my 2023 MacBook Pro. The time machine back up takes up 98 GB on the thumb drive on the 2023 Pro but the 2025 Air wants to use 167 GB so it can't finish. The thumb drives are 125 GB. So it's good for the 2023 Pro but too small for the 2025 Air. Despite all of my research and checking settings on both, I cannot figure out where the difference is. I ultimately decided that if I can't get it done, I'll just use the TM back up from the 2023 Pro for the 2025 Air if it's ever necessary. But I would like for each to have their own back up. Anything important is in the cloud so I'm wondering if I'm just overthinking this whole thing and shouldn't worry about it.

MacBook Air 13″, macOS 26.0

Posted on Nov 3, 2025 1:39 PM

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User profile for user: D.I. Johnson
D.I. Johnson
User level: Level 7
31,337 points

Nov 3, 2025 2:02 PM in response to boerstj1

boerstj1 wrote:

[...] But I would like for each to have their own back up. Anything important is in the cloud so I'm wondering if I'm just overthinking this whole thing and shouldn't worry about it.

Each Mac should have its own TM backup on its own backup drive. Each TM backup drive should have a capacity that is 2X the capacity of the Mac's startup drive being backed up.


Thumb drives are not especially hardy nor generally have the build quality of any dedicated external HDD or SSD. Too often we hear of thumb/flash drives failing for no reason at all and without warning. (YMMV)



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Time machine back ups on 2 macs are different file sizes

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