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Can not mount, erase, or run First Aid on external Time Machine hard drive.

Time Machine partition on my 3TB external hard drive won't mount, First Aid fails, and I can't even erase it and start over. What can I do? The other partition (just files and such) is working fine.


If I run First Aid, I get:

Running First Aid on “Time Machine” (disk2s2)

Repairing file system.

Volume is already unmounted.

Performing fsck_hfs -fy -x /dev/rdisk2s2

File system check exit code is 8.

Restoring the original state found as unmounted.

File system verify or repair failed. : (-69845)

Operation failed…


If I try to erase it, I get:

Couldn’t open disk. : (-69879)

Operation failed…


I'd love to just be able to erase it and start a new Time Machine disk on the partition, but I can't even do that. If anyone can help me out, I'd be extremely grateful.

MacBook Pro 15", macOS 10.15

Posted on Apr 29, 2020 7:03 AM

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Question marked as Top-ranking reply

Posted on May 1, 2020 10:46 AM

Within Disk Utility you may need to click on "View" and select "Show All Devices" before the physical drive will appear on the left pane of Disk Utility. Select the physical drive and erase it as GUID partition and MacOS Extended (Journaled).

https://support.apple.com/en-us/HT208496

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4 replies

May 23, 2020 12:55 AM in response to thedodus

I had my machine returned from Apple after getting it fixed for a separate issue (new display) and had asked for a fresh osx install as well. When I got home and tried to run "restore from time machine", I encountered the issue where the time machine external drive was not mounted. It was showing up as greyed out in disk utility, and clicking "mount" did nothing, and clicking "first aid" returned the exact same results as you described above.


I googled a bunch and had read many similar topics where data repair was required and various other steps, but I couldn't risk formatting or running anything on my time machine drive because it has all my work on it.


This will sound crazy, but in disk utility, after clicking on the greyed out time machine drive, to the right of the "mount" and "first aid" buttons, there is an "i" information button. I clicked that randomly to see if it would tell me anything about my drive, and after loading for some time, it displayed a bunch of info (I didn't pay attention to what it said specifically) and incredibly, my time machine was mounted!


I'm now restoring....


I don't know what happened, or why, or what caused this, but I am incredibly relieved. I'm not sure if these were the symptoms you're experiencing but worth a shot?

Can not mount, erase, or run First Aid on external Time Machine hard drive.

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