Time Machine needs 11TB for a 1TB backup? Please help!

Question

Time Machine needs 11TB for a 1TB backup? Please help!

Whenever I run the time machine from my 2020 iMac running Big Sur, it says that the backup needs 11 Terabytes to complete the backup. (Sometimes it reads 9 TB etc. It changes but it's always massive!)

Therefore it says my 2 TB disk is insufficient (see image). But there is only 700GB on my entire drive, which is only 1TB anyway. How can this be?

For the record, I have tried:

rebooting the machine and disks
changing and erasing all backup disks
using 2TB, 4TB, SSD and USB3 versions, all freshly formatted APFS
locating any local snapshots and deleting them all

Time Machine Error

I can't locate any big files on the Mac, even misread ones. In Explorer, the 1TB drive lists 315GB of space.

Desperate for an answer here!

iMac Spec

Posted on Jul 19, 2021 7:40 AM

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Answer 1

den.thed

Level 10

82,444 points

Jul 19, 2021 8:03 AM in response to JasonDynamics

Sounds like Time Machine maybe trying to "Include" the other external drives connected to your iMac.

To "Exclude" the other external drives from your Time Machine backups. Go to Apple > System Preferences > Time Machine > click the Options... button > click the + box and Add the other external drives to the Exclude these items from backup: list.

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Answer 2

Jul 19, 2021 8:32 AM in response to den.thed

Hi, thank you for the reply; I think you might be onto something here.

I re-checked the excluded discs (I even added Dropbox!) but all my other disks were on there - except one. I have a second 14 TB backup drive that was not on the excluded list but when I tried to add it, it would not let me select it, which was odd. So I unplugged that drive completely and tried the TM backup again and it looks like it's going to work!

Thank you again for the pointer, I will post if it is successful.

Jason.

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