Splitting Fusion Drive on 2017 iMac running Mojave

[casperes1996]

FD APFS is supported only under Mojave. Splitting and removing partitions destroys data and is time consuming but not hard since wiping and reformatting the system is easy. Removing partitions and containers while keeping data intact is quite time consuming as it involves moving data between partitions, alternating between Disk Utility and Terminal Commands till the desired result is achieved. All while hoping that you don't hit the wrong command and have to start from scratch anyway... It's difficult but I've done it on test a drive to see for myself and will never do so again.

What about the procedure is any easier under a CoreStorage system though? It's not like you can split a CoreStorage Fusion Drive without data loss

 

[rc705]

If you're going to replace the HDD with a 4TB 860 EVO, you should consider re-tying it back into the 128G as a Fusion Drive. Seriously, like old Ron Popeil: "Set it and forget it".

Oh! I actually like that idea of making them into a fusion drive. Great suggestion! =)

Funny side story, I just received my 4TB SSD in the mail today and I opened it up only to discover a 250GB SSD. What?? Someone at the warehouse must have swapped it out and took the 4TB home. CRAZINESS!!! Returned it for a replacement, but now I'm just hoping i'll get a new drive back, and SOON!

Set it and forget it! Ron was awesome!!

 

[rc705]

HI EVERYONE!

Just wanted to post an update. I got everything installed and it works great! There was no need to split the fusion drive before installing everything. Once the HDD drive was pulled out and the SSD was installed it automatically split it from the Blade drive. A fresh copy of Mojave was installed on the 128GB Blade along with my applications/fonts, and everything else, including my user folder, is on the new 4TB SSD. Also, the tech who did this for me said you can't create a Fusion Drive between two SSD drives so that option was out. They also installed a heat sensor.

Now I have an extra 3TB HDD that was in the iMac originally. I might just use that for a redundant backup of my backups for anything important.

This 2017 iMac may be older, but it's blazing fast from what I was on last (2010 iMac with an SSD). 4K video projects that were taking 60min to render out now take 1min. AMAZING. The workflows seems the same, but the render time is amazing.

So now my specs are 2017 iMac 4.2 i7, Radeon Pro 580 8GB, 128GB Blade, 4TB SSD and 64GB of RAM (which I installed myself). Then I'll be running a 3TB RAID from two old SSD drives and now I have that extra 3TB HDD that I can use as a redundant backup. Spent a total of around 3K for everything. I could have bought a new 2019 iMac, but it would have cost me another 1K, which I don't have and this set-up should last me a good 5 years. I'm HAPPY! =)

Hope this info helps for anyone wanting to upgrade their old Fusion Drive machines!!!

 

[casperes1996]

Also, the tech who did this for me said you can't create a Fusion Drive between two SSD drives so that option was out.

The tech is wrong about that. macOS may not be able to automatically assign roles to the drives, but you can do it regardless, and you can manually tell macOS which drive is the main (fast SSD) and which is the secondary (slower SSD).
The command is
diskutil apfs createContainer -main [diskID] -secondary [diskID]