Trying to replace the 1TB HDD on a Retina 4K Display (2017) iMac 21.5", Fusion Drive with a Crucial 1TB SSD.

[eogold]

I am trying to replace the 1TB HDD on a Retina 4K Display (2017 iMac 21.5”, Fusion Drive, with a Crucial 1TB SSD.

— I backed up the machine with Time Machine
— Booted into Recovery Mode to use Terminal commands to split the two drives into a 28GB blade SSD and a 1TB HDD
— I opened up the iMac and replaced the HDD with the Crucial 2.5" SSD
— I booted the iMac from an external macOS 12.5 installer drive and tried to format the SSD using Disk Utility. But whether I formatted it as HFS+ or APFS, it would fail validation (via First Aid)
— To test if it was a bad SSD, I connected the SSD (using an external enclosure) to another Mac running macOS 12.5 and reformatted the drive successfully as either HFS+ or APFS. I then successfully installed macOS 12.5 on the SSD and successfully booted the Mac from the SSD. I also successfully booted the 2017 from the SSD in an external enclosure. So I know I have a good SSD that WILL boot this iMac
— However, when I connected the SSD to the iMac’s internal 2.5” bay it would not even “see” the above SSD and obviously would not boot — However, it DOES “see” the original 1TB HDD

Any thoughts about what I need to do on this 2017 21.5” Fusion Drive iMac to replace the HDD with an SSD?

 

[zarmanto]

Sounds like you must have missed a step when splitting the drives. Which how-to did you follow? A quick trip to google seems to suggest that there are quite a few steps.

 

[eogold]

Yes, I successfully used the following command to break apart the Fusion drive and reformat each drive as a Separate volume.:

diskutil apfs deletecontainer diskX (diskX = the name of the fusion drive logical volume)

Afterwards I was able to boot the Mac successfully with the old HDD in place, etc. The Mac clearly now sees those two drives as separate entities that could be formatted, etc. However whenever I swap my 2.5 inch SSD with the old HDD in the internal bay of the iMac, the Mac will not boot - the Mac does not see a drive attached to that internal connector, even though the same SSD will boot this Mac as an external drive.

 

[zarmanto]

Maybe it's time to try resetting the PRAM/NVRAM.

 

[eogold]

Already did that numerous times - no help.

 

[macguru9999]

I have done literally dozens of these jobs without a problem, BUT not a 21.5 fusion mac. The regular 21.5 , i have put crucial mx drives in them, the older 2012-5 27ins too, and if fusions then i usually leave the little ssd in place and ignore it, or format it as a scratch drive etc. could the 2017 fusion be different ? i dont know but i dont think so. this has me intrigued. You should pull the motherboard and fit a 1tb nvme blade in an adapter to the back of the mobo and try it without a sata ssd installed. verify that its working. then try a different sata ssd in there as well and try that. I dont think there is any special firmware stopping you but i suppose i could be wrong ...

 

[eogold]

I have done literally dozens of these jobs without a problem, BUT not a 21.5 fusion mac. The regular 21.5 , i have put crucial mx drives in them, the older 2012-5 27ins too, and if fusions then i usually leave the little ssd in place and ignore it, or format it as a scratch drive etc. could the 2017 fusion be different ? i dont know but i dont think so. this has me intrigued. You should pull the motherboard and fit a 1tb nvme blade in an adapter to the back of the mobo and try it without a sata ssd installed. verify that its working. then try a different sata ssd in there as well and try that. I dont think there is any special firmware stopping you but i suppose i could be wrong ...

I have also done many, many of these HDD/SSD replacements, but never with an iMac with a Fusion Drive before. It feels like there is some sort of firmware that is preventing the Mac from properly communicating with a non-HDD connected to the internal 2.5" connector.

I thought about upgrading the nvme blade instead but that involves removing the motherboard and that's way too many steps/time investment for me to reasonably charge my client for this upgrade.

 

[macguru9999]

eogold I have done 3 or 4 27" imacs 2012-2015 with fusion drives and just left the 128g ssd in place with no problems... thats why i am skeptical about the 2017 21.5 being different , but these are pretty rare thats why I have not done one before. I agree its not economical to swap the blade for a client unless they pay lots more Its more something I might do on a personal computer. One thing you could try is formatting the crucial sata ssd and the 28g blade together AS A FUSION DRIVE and see if that works. There are plenty of instructions for the unix commands online and it looks like you have a good excuse to try. Also I would not do anything in monterey try formatting the drive with an older os even before you try the fusion thing