Fusion Drive replaced now seeing circle with line through it

[DoNoHarm]

Hello everyone,

I have a 2015 iMac 27” desktop whose Fusion Drive finally died. I replaced the 2TB HDD part of my Fusion Drive with a 2TB SSD but when I try to boot, I get the screen that shows 'support.apple.com/mac/startup' with the circle with a line thought it.

I imagine I have to do something like set it up on disk utility, but I was wondering if someone out there can help point me in the direction of the best way forward. Like is it better to create a new Fusion Drive with the SSD or should I just use the SSD only? And how do I configure everything to do this? Thanks in advance!

 

[Bigwaff]

When you separated the Fusion Drive internal SSD+HDD combo, you destroyed the file system. You either need to boot from Internet Recovery or a bootable USB Mac OS Installer. Once booted, use Disk Utility to reformat the drive(s). The internal SSD (which is typically very small capacity 32GB/64GB) and the 2TB SSD (if installed correctly) should appear in Disk Utility as two separate drives. Creating a Fusion Drive using both is possible but kind of a goofy thing to do. The point of the Fusion Drive is to use the internal SSD as a cache for the most frequently accessed files because a HDD is so much slower. Replacing the HDD with an SSD mostly defeats the purpose of the Fusion Drive cache feature. I recommend you set up the internal SSD and 2TB SSD as separate drives and use the 2TB SSD as your boot drive.

 

[DoNoHarm]

Kind of amazing, I needed some more info, so I just put the question to chat gpt and got amazing answers. Actually, I hit a few new roadblocks and it was like I had a dedicated tech support person there with me. Simply amazing. It’s a new world.