E2E process to split fusion and replace HDD with SSD on iMac

[Brianh9]

I've read various articles to split fusion drive and also replace HDD with SSD on my Late 2014 27" iMac but still not sure of the end to end process.

Do I split fusion first or replace HDD with SSD? When in the process is the bootable SSD Portion created?

 

[Taz Mangus]

I've read various articles to split fusion drive and also replace HDD with SSD on my Late 2014 27" iMac but still not sure of the end to end process.

Do I split fusion first or replace HDD with SSD? When in the process is the bootable SSD Portion created?

I would split the Fusion drive first. You select the boot drive from System Preference Startup Disk.

 

[Fishrrman]

Which version of the fusion drive do you have?

For the 2tb version, if you "split" the drive, you'll have a 128gb SSD and a 2tb HDD.
I'd just leave the drives "in place".
I'd set up the SSD with the OS, apps, and accounts -- MINUS any large libraries, such as music, movies and pics.
I'd leave the large libraries on the internal HDD -- they are seldom-accessed and even when used don't generally required "speed".

If I wanted more high-speed storage, I'd just plug in an EXTERNAL USB3 SSD and be done with it.
No risk of breaking anything inside that way.
The ONLY time I'd consider opening the iMac was if the internal HDD failed.