Time Machine - "couldn't unmount disk"

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Time Machine - "couldn't unmount disk"

I bought a USB flash drive to use for Time Machine. Worked initially, but then suddenly Time Machine no longer recognized the drive (or the partition, can't remember), and indicated it was an invalid disk. So, I have erased and re-partitioned the drive, but not Time Machine fails to prepare the disk with the message, "couldn't unmount disk". I can unmount the disk manually, using Disk Utility, but then Time Machine can't see the disk to use it. This is a fairly fresh install of MacOS 11 Big Sur, with hardly anything installed on it.

MacBook Pro

Posted on Dec 12, 2020 6:15 AM

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Answer 1

Joseph_S.

Community Specialist

Dec 16, 2020 7:49 AM in response to laurinkdavis

Hello and welcome to Apple Support Communities, laurinkdavis.

If we understand your post correctly, you're unable to create a Time Machine backup because Time Machine doesn't not recognize the drive you're using. We’d like to help.

Follow the steps in this article:

If you can't back up or restore your Mac using Time Machine

Let us know if that resolves this issue for you.

Thanks for using the Apple Support Communities.

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Answer 2

laurinkdavis Author

Level 1

12 points

Dec 17, 2020 4:26 AM in response to Joseph_S.

No. That was true at one point, but I did it get to recognize the disk, but it could not prepare the disk due to not being able to unmount it.

However, I abandoned trying to use a USB flash drive and have purchased an external drive instead - I don't have time to troubleshoot it anymore, thanks.

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Time Machine - "couldn't unmount disk"

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