Erasing and reformatting an exFAT external hard drive on Mac OS.

I have an exFAT formatted external hard drive that my Mac OS Monterrey on MacBook will not mount. I used to be able to use this hard drive fine. It appears in Disk Utility but as unmountable.

So I decided to erase the drive to reformat as a Mac OS Journaled but I've been unable to do is. Trying to erase on Disk Utility returns and Error after the progress bar says "mounting disk..." and trying to erase in Terminal gives an "Error: -69877: Couldn't open device".

I can read the drive fine on a PC (although it asks if I would like to repair it first), even though I created it on my Mac on a previous OS.

Any suggestions? thanks!

MacBook Air 13″, macOS 10.15

Posted on Jan 28, 2024 10:49 AM

Top-ranking reply

r_scheid

Level 3

899 points

Posted on Jan 28, 2024 2:47 PM

Hello! Try changing the partition scheme to GUID first. Make sure that you select the entire device in the sidebar of Disk Utility instead of just the partition. Then select Erase and you will be able to change the partition scheme. If you can't see the device and can only see the partitions, you can correct this In Disk Utility on your Mac, choose View > Show All Devices.

If this doesn't work, I would also try performing the tasks through Disk Utility on the recovery volume.

Hope this helps!

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Erasing and reformatting an exFAT external hard drive on Mac OS.

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