Can't upgrade to Mojave on iMac with SSD

First of all do a full clone of your drive to an external drive, using SuperDuper or CCC. Also have an up to date Time Machine backup.

Make sure your can boot from the clone and works correctly.

Download the Mojave installer (in this case apparently you already have it) and follow the available instructions to create a bootable installer on a thumb drive.

Boot from this thumb drive, erase your internal SSD and install.

You can choose at this point to migrate your user accounts from the clone or do it later by running Migration Assistant from your new Mojave system.

Complete the TM Backup first. After it is complete, then...

Restart the Mac, into Internet Recovery, and use the following steps as a reference. Once in Terminal, we need to erase both internal physical disks. Booting in Recovery can renumber disks, so we need to be careful on the next steps. If you run diskutil list, you will see two internal drives. One is your 121GB SSD part, the second is your 1TB EVO. I will call the SSD as disk0, and EVO as disk1. If they are different, adjust the steps accordingly.

Steps should be

• Erase the CS LV - diskutil cs deleteVolume 01F26C59-3460-407E-B34B-5F6ED151DA82
• Erase the CS LVG - diskutil cs delete 14F70A2B-67C8-43EC-B1DF-B1B31FBDD088
• Erase the SSD - diskutil eraseDisk jhfs+ SSD disk0
• Erase the HDD - diskutil eraseDisk jhfs+ HDD disk1
• Create the Fusion (CS) Volume Group - diskutil cs create macOS-LVG disk0s2 disk1s2 (please ensure the SSD is first).
• The previous step will output a long string similar to the following (CS LVG UUID), which I will use as an example.

  F5D64E6C-7796-48E9-955E-46429D58A9BF

• Create the Fusion (CS) Volume -
  • diskutil cs createVolume F5D64E6C-7796-48E9-955E-46429D58A9BF jhfs+ "Macintosh HD" 100% .
  • The "100%" allocates the entire capacity of the two combined drives to "Macintosh HD".
• Post the output of diskutil cs list, before we go further.

You can post the output of the Recovery Terminal session (although it is a bit tedious) as noted in Posting Text Output in macOS Recovery Console .

Mojave Installer is confused with two SSDs, so we will help the installer a bit. Boot from the USB Installer, and start Terminal.

We need to create an APFS container manually, and then install Mojave and restore your user content (settings/apps/files etc.).

Steps should be

• Erase the CS LV - diskutil cs deleteVolume <Put-the-Current-CS-LV-Here>
• Erase the CS LVG - diskutil cs delete <Put-the-Current-CS-LVG-Here>
• Erase the SSD - diskutil eraseDisk jhfs+ SSD disk0
• Erase the HDD - diskutil eraseDisk jhfs+ HDD disk1
• Create the APFS Fusion Container

  diskutil apfs createContainer -main disk0s2 -secondary disk1s2 (please ensure the SSD is first).

• Post the output of diskutil apfs list, before we go further. We should let the Installer create volumes, as it sees fit.

This is the man page for the command used.

diskutil apfs createContainer

Usage: diskutil apfs createContainer <disk> [<disk>]

diskutil apfs createContainer -main <disk> [-secondary <disk>]

where <disk> = MountPoint|DiskIdentifier|DeviceNode

Create an empty APFS Container. You can then add APFS Volumes with the

diskutil apfs addVolume verb. If you specify two disks, then a "Fusion"

Container is created, with the performance roles assigned automatically

unless you use the -main and -secondary options, in which case, the secondary

disk is assumed to be on "slower" hardware which is preferably not solid

solid state, usually larger, and often used to store associated "auxiliary"

data such as the Windows partition(s) for Boot Camp Assistant.

Ownership of any affected disks is required.

Example: diskutil apfs createContainer disk0s2

This CS LV/LVG is incorrectly built. The smaller SSD (119GB) should be at index 0, instead of the 1TB EVO. If you have a TM backup, this Fusion drive should be first rebuilt, restored from TM, before you attempt Mojave upgrade.

Was the EVO an after-market replacement?

Since your Container disk is disk3, use the following commands...

• Add additional volumes (assuming disk3 is the container, change as appropriate)
  • Preboot - diskutil apfs addVolume disk3 apfs Preboot -role B -reserve 1g
  • Recovery - diskutil apfs addVolume disk3 apfs Recovery -role R -reserve 1g
  • VM - diskutil apfs addVolume disk3 apfs VM -role V -reserve 1g
• Post the output of diskutil apfs list before we go further. The role value must be uppercase.

Can you post the output of

diskutil cs list

It would be good to know if the CS is revertible or not?

How to fix a split Fusion Drive - Apple Support

Can you post the output of

diskutil list

from macOS Terminal?

If your

diskutil cs list

has not changed, this looks like a bug in the Mojave Installer, which is confused by two SSDs in a CS and does not know how to convert it to APFS.

Do you have an external disk which is 32GB or larger which can be erased and used to temporarily install Mojave?

We know there are issues with the CS conversion, so that is not a worthwhile option to pursue.

We should go back to APFS, but this time we can add standard volumes, including Recovery, PreBoot and VM in addition to Macintosh HD and test installation.

Very underwhelmed by the rush to get APFS Fusion out of door, and leaving gaping holes in functionality.

Instead of an image, can you copy the Terminal output and paste it as a reply?

Can you boot from the Mojave installer and try to install it on the Fusion Container?

heatherfromashburton wrote:

It is a Samsung SSD 850 EVO 1TB installed with an Apple SSD controller SD0128F.

That's what I thought. It seems for whatever reason, Mojave does not want to install on those drives. At least it's been reported a number of times.

Looks good. Now you have two choices,

• Either install Mojave on this clean CS LV/LVG, and restore your TM backup (User settings, applications, and user files), or,
• Restore full TM, which will put the Mac in the same state as you started with after the last TM backup, and then upgrade to Mojave.

You decide!

You can also try both, but it may take a while.