27" iMac (Late 2012) Blade SSD Upgrade Question

[Flipme]

So first things first I have already performed the upgrade and all is well with one exception. Prior to performing the upgrade I did not decouple the fusion drive. I've since read that was a good first step...now the machine doesn't detect the HDD. It only detects the new blade SSD. I've installed Catalina and all is well except the HDD. I'd like to enable the HDD for the extra internal storage without coupling the new Blade SSD and the HDD. I'm open to any suggestions. So far I've tried:

• detecting the HDD from Disk Utilities
• listing the linked drives via diskutil from terminal (doesn't exist)
• listing the linked drives via diskutil from terminal in Recovery Mode (doesn't exist)
• Swapping the HDD with a known good HDD

My googlefoo has failed any further ideas and I'm at a loss. I'm going to do a PRAM reset and then boot to safe mode and see if I get any other result. I'll update if I get any further. I'm open to suggestion. The 2.88 TB disk listed on the attachment is external.

 

[nambuccaheadsau]

You can re-create the Fusion Drive by doing the following. If still no joy maybe the platter has failed, usually what happens to Fusion Drive models when a drive quits. DU not showing the drive is not good.

How to fix a split Fusion Drive – Apple Support (AU)

If your Fusion Drive appears as two drives instead of one in the Finder, it’s no longer working as a Fusion Drive. Here’s how to fix it.

support.apple.com

 

[Flipme]

You can re-create the Fusion Drive by doing the following. If still no joy maybe the platter has failed, usually what happens to Fusion Drive models when a drive quits. DU not showing the drive is not good.

How to fix a split Fusion Drive – Apple Support (AU)

If your Fusion Drive appears as two drives instead of one in the Finder, it’s no longer working as a Fusion Drive. Here’s how to fix it.

support.apple.com

I do not want to re-create the fusion drive. I'd agree about it not being good that DU isn't showing the drive. PRAM reset and Safe Mode didn't fix it or reveal anything (not surprising). I guess it possible I killed the SATA controller. But..the Serial-ATA Device Tree lists the functioning SSD but nothing about the HDD. It is worth noting that I triple checked the SATA cable prior to re-assembly.