TimeMachine estimated size of full backup

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TimeMachine estimated size of full backup

I have a test partition on a 500GB HDD running High Sierra and I thought it would be a good idea to have a backup. The HDD has 340GB free space and as such only 160GB is used. And I have a small 300GB HDD that I would use, but TimeMachine tells me "not enough capacity" and I can see that it calculates the size for a full backup of the 160GB to be 809GB!!!!

My Mac has a 1TB HDD and is using 648GB and here Time Machine calculates the size for a full backup to be - yes you're right - 648GB.

So what am I missing? Can anyone explain this?

iMac, macOS 10.12

Posted on Dec 18, 2020 8:53 AM

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Answer 1

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johpo01 Author

Level 1

49 points

Dec 18, 2020 2:21 PM in response to BDAqua

Spot on. If you boot from an external HDD and run Time Machine, then Time Machine will default include your internal HDD. So you'll have to exclude it in "Options".

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