NVME M.2 SSD with adapter
Is it possible to update 2017 iMac 27" 5k with NMVe m.2 SSD using m.2 to Apple PCIe adapter?
I used to use SM951 AHCI in Mac Pro 5.1, 6.1, all Retina and Air 2013-2015 but what about NVMe once? Have anyone tried?
First you may want to look at this Vid: 2017 27-inch iMac with Retina 5K Display Unboxing and Teardown jump to the 10:00 time point which shows the PCIe SSD Apple is using. It's very different from the M.2 SSD's.
Apple's PCIe NVMe SSD's use a custom device driver so while you might be able to get the adapter and NVMe SSD to physically fit it won't be recognized by the OS.
While I haven't tried anything in this new iMac I can tell you I've tried the newer MacBook Pro retina series which has a 2 lane NVMe SSD and it didn't work.
I already bought 512 GB Samsung Pro 960 M.2 SSD. After I disassembled my iMac 2017 27". I'm shock realizing the interface is different! I feel stupid.
I'm ordering the adapter which is about 1 month to arrive. =( I'll buy the adapter to SATA for now and use it as storage. Later on I'll buy the correct SSD and install the OS on it.