Splitting fusion drive help

Thanks. As best I can tell you have two physical drives - a 1TB HDD (disk1) and a 128GB SSD (disk0). Are you sure the HDD is failing? How did you determine that?

You can do the following:

Open Disk Utility and set the View dropdown menu to "Show All Devices."

Install El Capitan or Later from Scratch

1. Restart the computer. Immediately, at or before the chime, hold down the Command and R keys until the Apple logo and progress bar appear. Wait until the Utility Menu appears.
2. Select Disk Utility from the Utility Menu and click on the Continue button.
3. When Disk Utility loads select the SSD (out-dented entry, Apple SSD...) from the Device list.
4. Click on the Erase button in Disk Utility's toolbar. A panel will drop down.
5. Set the partition scheme to GUID.
6. Set the Format type to APFS (SSDs only.)
7. Click on the Apply button, then wait for the Done button to activate and click on it.
8. Quit Disk Utility and return to the Utility Menu.
9. Select Install OS X and click on the Continue button.

This will install the current version of macOS on the SSD. Upon completion, the computer should reboot from the SSD with the Setup Assistant. This will also break the Fusion Drive relationship with the HDD.d

What you've posted is not a full listing of the drives. Please open the Terminal and enter: diskutil list. Press RETURN.

Please post the results.

I believe you will need to reformat the SSD. Do you know what the SSD's capacity is? If your iMac came with a 1TB HDD, then the SSD may not be large enough to use in place of the HDD. My 2015 iMac came with a 1TB HDD and a 28GB PCIe SSD on which only macOS was installed.

SM800 Said:

"[...]I just want ALL of my content and OS on the SSD only without the HDD being accessed or relied upon at all. In my mind, the HDD should just be a physical component there but not used whatsoever. I have an install of Catalina on my external SSD currently so once I can get the SSD to stand alone by itself, my plan was to go and re-install OS on the SSD."

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Unmount the Disk:

So, if all is as it should be on the SSD, and nothing is transferred...

1. Boot: into Recovery Mode
2. Go to: Disk Utilities
3. Unlock: the Lock
4. Select: HDD
5. Delete: All Partitions
6. Format: the HDD
7. Unmount: the HDD

All should be set.

When using Disk Utilty, set View (Top-left of window) to "Show All Devices".

SM800 Said:

"Splitting fusion drive help: [...]I guess I could use an external boot drive if needed, but trying to do this internally if at all possible. Computer is just not useable as it is due to the issues with the HDD so I need another solution."

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Splitting or Consolidating?

So, do you want to consolidate these? Or create two "drives"? Partition this drive if you want to split it. Just let it stay as one partition, if you do not want to split it, but rather merge it. Perform either method in step two.

Reinstall the macOS Anew:

Try This:

1. First, Backup your Mac, then
2. Then, install your macOS Mojave anew.
3. Finally, migrate it over.

In Depth:

1. Back up your Mac:

Start by, creating a Time Machine backup of your Mac, so that you can have something to restore your Mac from, should anything go wrong with the reinstall.

2. Use a USB Bootable Installer:

Create a USB Bootable Installer for macOS. Delete the hard drive's partitions. Then, install this macOS with it. Go Here: How to create a bootable installer for macOS - Apple Support.

3. Migrate and Reinstall Data and Apps:

Next migrate it over from the Time Machine Backup you created in step 1 to this new install. If required, request from the developers new keys for the software, informing them that your computer crashed. Ask for 64-bit installers, if looking to install Mojave and upgrade thereafter.