Trying to replace the 1TB HDD to 1TB SSD

Update:I have now tried to get this process working with:

-- 4 different 2.5" SSDs

-- 3 different HDDs

In NONE of the above cases have I been able to successfully format the replacement drive in the internal bay, either using DiskUtility to format the drives as separate or using the "resentFusion" Terminal command to create a new Fusion drive.

-- The ONLY thing that has worked is putting the ORIGINAL Apple HDD back in. Then using resetFusion recreates the Fusion drive and I can re-install the macOS. But the whole point of this endeavor was to swap the original Apple HDD with a faster drive (either an SSD or a Seagate 7200 RPM HDD). The conclusion I have reached its that there is firmware somewhere that requires an Apple-branded 2.5" inch drive.

I have not tried removing the blade SSD because that would be uneconomical for my client. I am willing to consider removing the the blade SSD if I know for sure that will be successful. But it sounds like we don't know that for sure?

@ericogold - Sadly you still have the TP stuck to your shoe still!

The blade SSD is a cache drive which is married to the original HDD. To break this you need to format the blade SSD so it can't confuse things, that is if you want to leave it in.

I have used terminal commands to break apart the fusion drive and reformatted the blade drive several times. Despite this the Mac still balks at a normal successful formatting of a 2.5 inch drive on the internal connector unless it’s the original drive that Apple put in.

I’m wondering if there’s some additional terminal command that I need to issue to make the Mac completely forget it ever had a Fusion Drive.

I’m wondering if you are correct that the simple presence of that Apple play Drive in the machine prevents me from using anything in the 2.5 inch connector except the original Apple Drive.. What if the internal drive failed and Apple had to repair this machine by replacing that 2.5 inch drive? Is there something about an Apple-branded 2.5” drive that makes this all work?

@ericogold - Different macOS's releases do things differently!

I don't even bother with the Terminal commands as they often don't work (which is clearly one issue here). I always pull the blade SSD, as my clients want the speed of the PCIe/NVMe interface not the slower SATA III (6.0 Gb/s).

As you can see here the SATA drive is a straight drive replacement with either a 2.5" HDD or SSD iMac Intel 21.5" Retina 4K Display (2017) Hard Drive Replacement

The only issue you face is the SSD Cache drive is getting you in trouble iMac Intel 21.5" Retina 4K Display (2017) Blade SSD Replacement

Dan,

In this case my client is a woman in her 80's whose 21.5" iMac has a failing 2.5" HDD and who just wants a slightly faster Mac. The extensive work to remove the blade drive makes labor cost prohibitive for her. Have you had any direct experience with this situation on a 2017 21.5" iMac? I'm willing to eat the cost of removing the blade drive, but it sounds like you aren't sure that will solve the problem (allow me to successfully replace the 2.5" drive with a 2.5" SSD).