Mojave macOS Installation Error (com.apple.DiskManagement error 69854)

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?

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!

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.

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)