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I want to upgrade my 1 TB Fusion Drive to SSD. Majority is suggesting that I do it with Samsung 860 EVO because Samsung 970 EVO has M.2 and that is not compatible with my iMac. But there’s too much performance difference between Samsung 860 EVO and Samsung 970 EVO. Can someone enlighten me in detail:

  1. Is it doable ? How can it be done ?
  2. When done, will there be any issues that would effect the daily usage of my iMac?

Apple uses a custom SSD which while similar to the M.2 blade drives but are different! Here’s a good reference: The Ultimate Guide to Apple’s Proprietary SSDs Here’s the guide you’ll need to follow: iMac Intel 27" Retina 5K Display Blade SSD Replacement and here’s one source of the correct SSD BeetsTech - 512 GB PCIe 2.0 x2 SSD drive But! Before you even open the system you’ll need to break the Fusion Drive set following this guide: How to split up a Fusion Drive As far as performance differences between Samsung 860 EVO Vs Samsung 970 EVO has to do with the different drive interfaces between the drives and the technical improvements within the drive its self. Lastly, the number of lanes the drive offers and what the system can support. Your system only supports two PCI/e/NVMe lanes.

In any case … Given the difficulty getting to the systems SSD connector I strongly recommend you stick with the proper Apple SSD. I know some folks have fitted M.2 SSD’s into MacBook Pro’s. We gave it a try and I’ll tell you its not worth it! Too many issues some you just can’t over come.