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I would not recommend using an APFS formatted HDD for Time Machine. It's painfully slow. With my Samsung T7 the hourly Time Machine backups are usually finished after a couple of minutes. Using my older HDD they can easily take 20 minutes to half an hour.

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While time machine used to be snappy on HDD it was build out of one of the weirdest little hacks hard links in folders. The new Time Machine might front a similar front end but under the hood its a different beast. You're having to mount snapshots as you move through time.

are you sure that is because of apfs? hdds are usually much slower, no?

It's definitely APFS. I've had the pleasure* of HFS+ and APFS on the same external HDD and APFS is horrible. Given it is optimised for solid-state drives[0], it's understandable there'd be some slack but it is absolute horse paste.

(If I could create an encrypted external HFS+ volume, I would but macOS hasn't allowed that for a while as far as my experience goes - it's non-encrypted HFS+ or encrypted APFS.)

[0] https://support.apple.com/en-gb/guide/security/seca6147599e/...

My point is that while the old HFS+ based Time Machine was performing ok on spinning disks, the new APFS based TM backups are excruciatingly slow and take ages to finish. I did actually compare both types on the same hard drive and even then the difference was very obvious.

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