I tried upgrading from High Sierra to Mojave on my MacBook Pro mid-2012 Non Retina, 16GB RAM and 500GB HDD, core i7. Unfortunately I don't have a backup and I keep getting this error "com.apple.DiskManagement error 69854" during the installation. I can only access into Recovery.

How can I solve this error and install Mojave without losing my data?

  • boot from USB drive, try to repair your disk ! – Ruskes Sep 25 '18 at 22:37
  • Hi Ashraf. What support do you want? Please edit the question to explain if you need help making a backup or you can lose all the data and just want to know how to wipe and reinstall. – bmike Sep 26 '18 at 0:27
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    I ran into the same issue. Trying to convert to APFS manually in recovery mode also yields an 69860 error. Do you have partitions / bootcamp? – Xster Sep 26 '18 at 0:28
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    Thank you for your answers, I want to install Mojave without losing my data @bmike since it's not possible to downgrade to High Sierra anymore. This error is appearing during the installation. – Ashraf Sep 26 '18 at 7:08
  • I don't have partitions or bootcamp @Xster – Ashraf Sep 26 '18 at 7:09

Faced the same issue. "Lucky" for me, I faced an installation issue on my MacBook Air when installing High Sierra, so had to create an install USB drive (google on how to do so) and also wiped out SSD content. Of course, I was able to boot into Target Disk Mode and copied documents into my iMac. Now when upgrading to Mojave on my iMac, face the same problem as you. Create USB boot for High Sierra installation, boot from USB, and reinstall High Sierra. Twice in a row means I will not try upgrading OSX for a long time! Many hours wasted!

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  • This worked for me, I didn't wipe my data, I googled how to install High Sierra from USB and it worked. Thank you so much. – Ashraf Sep 26 '18 at 20:30

Had the same issue. Retina 5k imac. Rebooted with cmd-r and restored from time machine. Everything is back and working even boot camp!

Will be waiting before trying Mojave again.

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  • I will make a backup for sure so this won't happen again, do you mean that Mojave won't work for us? – Ashraf Sep 26 '18 at 20:31

Same issue as reported by others on this thread. Did also have issues installing High Sierra, my issue now is I cannot obtain a High Sierra image to make the bootable USB drive.

I dont have any real data on the machine so I'm wondering if a clean USB install of Mojave will work (that's how I got High Sierra on finally when that came out).

Another note with regard to my Macbook Air that's having this problem is that it's a fusion drive (128Gb onboard HD that came with it and a 128Gb SD card in the slot)

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  • Hi, welcome to the site! Just for future reference, things like this would probably be better as comments, once you gain enough reputation to post them. (Of course, you can't comment yet, so don't stress! (: You can always comment on your own questions/answers, though.) You get rep by having people upvote your questions or answers. – SilverWolf - Reinstate Monica Oct 3 '18 at 21:12

Resized my partition after the restore and installed Mojave on that partition without any issues. Right now I am thinking that the best way is to create a bootable Mojave USB installer and then erase my high sierra install and install Mojave on that empty disk later using the migration tool to bring back my apps and data from time machine.

I am worried that I will lose access to my bootcamp partition.

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  • Look one comment above. I did just like you creating a USB bootable and did not even need to erase high sierra. Did not lose my bootcamp either. – Jonathan Gauthier Sep 30 '18 at 23:45

Found a way to install Mojave without starting from scratch.

I created a bootable USB from those instructions: https://www.macworld.com/article/3284378/os-x/how-to-create-a-bootable-macos-mojave-installer-drive.html?page=2

Then simply installed Mojave over my existing high sierra. It did not work directly but it works from the bootable USB. My bootcamp partition is still there and usable too.

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    Hey Jonathan, which year model is your Retina 5k iMac? – Ashraf Oct 1 '18 at 8:26
  • Not sure of the exact year but it's from the first year there was a retina 5k mac; about 3-4 years ago. – Jonathan Gauthier Oct 1 '18 at 12:12

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