Plan to reformat the internal SSD a s a stand alone drive and install a 4TB SSD in place of the HDD. This is fairly simple, but is there a way to couple the 2 SSDs as fusion? Probably best to just keep them as different drives and the 4TB as boot. Thanks.
iMac Line (2012 and Later)
Welcome to the Apple Support Communities.
Please do not replace any internal drives or components. iMac is not user-serviceable and attempting an unsupported repair or upgrade comes with great risk to permanently damaging the Mac.
For this reason, please use an external SSD. This comes with zero risk, as you just plug in a USB SSD to install macOS and migrate your data to. And, it is almost as fast as an internal SSD. For more info, instructions, and what external SSD to buy, please see: How to Setup and Use an External SSD as your Startup Disk on a Desktop Mac - Apple Community.
Also, please only post once. Let's stick to this thread instead of I am replacing the HDD with an SSD - Apple Community.
Jack
Welcome to the Apple Support Communities.
Please do not replace any internal drives or components. iMac is not user-serviceable and attempting an unsupported repair or upgrade comes with great risk to permanently damaging the Mac.
For this reason, please use an external SSD. This comes with zero risk, as you just plug in a USB SSD to install macOS and migrate your data to. And, it is almost as fast as an internal SSD. For more info, instructions, and what external SSD to buy, please see: How to Setup and Use an External SSD as your Startup Disk on a Desktop Mac - Apple Community.
Also, please only post once. Let's stick to this thread instead of I am replacing the HDD with an SSD - Apple Community.
Jack
There is no need to create a Fusion Drive of two SSDs. If a SATA based SSD is not fast enough, then replace the Apple SSD with an OWC SSD, but beware that Monterey won't install if a third party SSD is installed until after the Mac's firmware has been updated which is done by first installing Monterey while the original Apple SSD is installed.
Plus like @Jack-19 mentions, this iMac is very difficult to open up and work on. You risk damaging the iMac especially the glass/LDC Panel and possibly one of several delicate cables and connectors.
You're going to be better off booting from an external SSD if your internal drive is experiencing problems or no longer suites your needs. The drives are relatively inexpensive and the external boot works very well. You can still use the internal drive as purely storage if you wish assuming it's not damaged in some way..
I am replacing the HDD (in a fusion config) with an SSD on a late 2015 Retina Mac using Monterey OS X
