Imac 27 2017 nvme?

[TheSufle]

Could you tell me the maximum drive capacity I can install? Why doesn't my 2017 27-inch iMac detect the WD Black SN7100 4TB?

A WD SN770 1TB is currently installed, and it is working.

 

[niteflyr]

Mactracker shows that it was available with up to 2TB of flash storage.

 

[TheSufle]

So what? It also says there that the memory frequency is 2667 MHz, but I have 3200 MHz installed.
All this data is based on the time when only that equipment was available.

 

[TheSufle]

I have a 2TB storage drive, and it doesn't see that either.

 

[zgagato]

So what? It also says there that the memory frequency is 2667 MHz, but I have 3200 MHz installed.
All this data is based on the time when only that equipment was available.

21" imac 2017 works great with 3200 ram for over a yeat now. As for storage, maybe it is an adapter issue? iMacs are picky with nvme in general. I only use sata for big storage, nvme for system.

 

[benholt]

Two things that bite on the 2017 iMac slot with 4TB DRAM-less drives specifically:

The SN7100 is HMB (host memory buffer) — it borrows a chunk of system RAM to hold its L2P mapping table because there's no on-drive DRAM. macOS at the desktop hands over the HMB region fine, but the iMac's boot-time NVMe enumeration in the SMC/EFI path allocates a much smaller buffer, and on a 4TB drive the L2P is big enough that the pre-boot enumeration silently fails. That's why your SN770 1TB works — same architecture, smaller table. It's not the adapter, it's the boot-time HMB negotiation.

Second thing: even once macOS is up, some Sintech adapters on 2017 iMacs don't route PCIe reference clock cleanly enough for the SN7100's Phison controller to link-train at Gen3 x4. Check `system_profiler SPNVMeDataType` and look at the "Link Speed / Link Width" line — if it reports x2 or degrades, that's a clock signal integrity issue.

Easiest test: boot from a USB installer with the 4TB installed and see if it enumerates in Recovery's Disk Utility. If not, the drive is invisible before macOS is loaded and you'll never boot from it. WD Black SN850X or SK Hynix Platinum P41 in 4TB tend to be the safe picks for this vintage — both have on-drive DRAM.

 

[TheSufle]

Two things that bite on the 2017 iMac slot with 4TB DRAM-less drives specifically:

The SN7100 is HMB (host memory buffer) — it borrows a chunk of system RAM to hold its L2P mapping table because there's no on-drive DRAM. macOS at the desktop hands over the HMB region fine, but the iMac's boot-time NVMe enumeration in the SMC/EFI path allocates a much smaller buffer, and on a 4TB drive the L2P is big enough that the pre-boot enumeration silently fails. That's why your SN770 1TB works — same architecture, smaller table. It's not the adapter, it's the boot-time HMB negotiation.

Second thing: even once macOS is up, some Sintech adapters on 2017 iMacs don't route PCIe reference clock cleanly enough for the SN7100's Phison controller to link-train at Gen3 x4. Check `system_profiler SPNVMeDataType` and look at the "Link Speed / Link Width" line — if it reports x2 or degrades, that's a clock signal integrity issue.

Easiest test: boot from a USB installer with the 4TB installed and see if it enumerates in Recovery's Disk Utility. If not, the drive is invisible before macOS is loaded and you'll never boot from it. WD Black SN850X or SK Hynix Platinum P41 in 4TB tend to be the safe picks for this vintage — both have on-drive DRAM.

Thank you for the reply; I completely agree with you.