Question Configuring an NVME M.2 "stick" to the proper motherboard socket

[BonzaiDuck]

For me -- on these forums -- this may seem like a naive question. I was just a tad late arriving to the NVME party in late 2016. Samsung was just releasing the 960 models (as I remember). I had actually planned my computer build -- at first -- to use an SATA SSD for a boot disk. All the other aspects of my planning -- preparing the proper case, choosing fans, PSU, motherboard, RAM and processor -- were deliberate and reasonably wise (IMHO). But I had to make last-minute adjustment to the work-in-progress for NVME M.2 drives.

I really do try to study the motherboard manual that arrives with the retail box. Somehow I was slow to catch on for the distinction between M.2 SATA and M.2 NVME with the sharing of bandwidth between certain SATA drive plugs and U.2/PCIE ports, respectively. So I simply configured my board to allow the full number of lanes and bandwidth to the PCIE x4 slot at the bottom of the motherboard, bought myself an NVME PCIE x4 adapter, and avoided any uncertainty about BIOS configuration of the motherboard's own M.2 slots.

Yes -- I must be a slow wit. But I didn't have to go through any trial-and-error frustrations, either. Maybe they wouldn't have been big frustrations, but I avoided them without dispelling my own ignorance about the newer motherboards.

Now -- I know what I'm doing. I have a "workstation" board. I've got five PCIE slots that will run at least two as x16 allowing x8 for the rest. I'll only have a single dGPU in the top slot.

I don't bother with M.2 SATA sticks. I have two 1TB SK HYNIX NVME P31 "Gold" drives new in their packages. I'm going to add one of them to the motherboard's M.2_2 slot, leaving the other empty. This latter -- the M.2_1 slot -- seems to be for SATA configurations, because the M.2 drive shares bandwidth with SATA ports 1 and 2. The M.2_2 slot shares bandwidth with the U.2 double plug next to the six SATA motherboard ports.

"Shares bandwidth" is the potential issue. I know that I'll enter the BIOS and find an "Enable/Disable" toggle for U.2. Do I need to enable U.2 to make the M.2_2 (NVME) work? Or, by "sharing bandwidth", can I disable the U.2 expecting correctly that all the bandwidth will go to the M.2_2 slot? I know I must configure this latter M.2_2 slot as PCIE x4 -- or so I think I must -- because that setting seems to be part of the configuration for "U.2 bandwidth sharing". I don't think there's any other mode setting for the M.2_2 slot, but I can check again . . .

 

[Micrornd]

So I simply configured my board to allow the full number of lanes and bandwidth to the PCIE x4 slot at the bottom of the motherboard, bought myself an NVME PCIE x4 adapter, and avoided any uncertainty about BIOS configuration of the motherboard's own M.2 slots.

Now -- I know what I'm doing. I have a "workstation" board. I've got five PCIE slots that will run at least two as x16 allowing x8 for the rest. I'll only have a single dGPU in the top slot.

I don't bother with M.2 SATA sticks. I have two 1TB SK HYNIX NVME P31 "Gold" drives new in their packages. I'm going to add one of them to the motherboard's M.2_2 slot, leaving the other empty. This latter -- the M.2_1 slot -- seems to be for SATA configurations, because the M.2 drive shares bandwidth with SATA ports 1 and 2. The M.2_2 slot shares bandwidth with the U.2 double plug next to the six SATA motherboard ports.

"Shares bandwidth" is the potential issue. I know that I'll enter the BIOS and find an "Enable/Disable" toggle for U.2. Do I need to enable U.2 to make the M.2_2 (NVME) work? Or, by "sharing bandwidth", can I disable the U.2 expecting correctly that all the bandwidth will go to the M.2_2 slot? I know I must configure this latter M.2_2 slot as PCIE x4 -- or so I think I must -- because that setting seems to be part of the configuration for "U.2 bandwidth sharing". I don't think there's any other mode setting for the M.2_2 slot, but I can check again . . .

You may want to study the block diagram in the appendix of the manual further.
If I understand what you are trying to accomplish (using an i7-6700K and 3 NVMe drives) then - put the NVMe to PCIE x4 adapter in slot 3, put a NVMe drive in M.2_1 and do not use SATA ports 5 and 6, put a NVMe drive in M.2_2 and do not use the U2 port, place the video card either in slot 1 or 4 to allow x16 usage. That should maximize your limited bandwidth of both the board and CPU by not sharing any bandwidth. Both M.2 slots should be set for PCIe mode (if available in your bios or may be automagicly sensed)
You will have to check the bios, BUT almost all ASUS WS boards I've seen didn't need any further settings changed to not share or share bandwidth, they sensed it and did it automagicly.
Hope that helps

 

[BonzaiDuck]

It helps -- it is both a good and useful perspective. Somehow I thought that the M.2_1 slot -- sharing the bandwidth of SATA ports -- was for M.2 SATA drives. But -- hey! -- those SATA M.2's have either a B key or an M+B key. I'll convince myself by looking at the slot with a magnifier, but if you're right, that's also nice to know -- that I can use an NVME in that slot.