[SOLVED] (Solved) Samsung 990 M.2 running 4x2 instead of 4x4? - Asus ROG Strix Z790-I Gaming Wifi

[mikeyymonster]

Hi everyone,

I just built my first SFF PC with the specs below. I have 2 Samsung 990 M.2 NVMe drives (2TB and 4TB). The OS is installed on the 2TB and the 4TB is mainly for backup. The OS drive is installed on the CPU linked M.2 (top mount) and the 4TB backup is on the chipset linked M.2 (bottom). These are both gen 4 M.2s and the motherboard is capable of both Gen 5 and Gen 4 (CPU gen 5, chipset Gen 4).

The issue is when I run the Samsung software for benchmark, I noticed my 2TB was about half the speed of the 4TB. When reviewing the interface, it shows the 2TB slower drive as 4x2 vs 4x4 on the 4TB. I've read that this can sometimes be caused by the M.2 not being properly seated as this particular motherboard doesn't have a screw for the M.2 drive in question. I've reseated it multiple times already and confirmed that is not the issue. I've also swapped the M.2 drives and whatever drive is in the top slot automatically gets the slower 4x2 speed, so the issue is not the M.2 drives. I have nothing else connected to the motherboard other than a RTX 4090 and memory.

Interestingly, I found a section in the bios under PCI Express configuration that indicates x2 under the slot in discussion, but it doesn't allow any changes. The only option it allows is whether you want to switch between Gen 1, 2, 3, or 4. It is currently set to 4. I'm thinking maybe they need to release another bios update and maybe this is related to the 14th gen CPU. Any thoughts?

• Asus ROG Strix Z790-I Gaming Wifi
• Intel 14700K
• 990 Pro 2TB NVme
• 990 Pro 4TB NVme
• RTX 4090 FE
• GSKILL 32GB DDR5

 

[thestryker]

The SSD plugs into a little riser card on that board right? It's possible the slot/card is damaged or was always faulty in that case.

The only other thing I can think of would be manually setting the PCIe slot to x16 in the BIOS which forces the M.2 slot to run off the chipset though I have my doubts about whether or not this will do anything.

 

[mikeyymonster]

Yes, it does have a riser, I suppose that could've been damaged. I will have another look at that when I take it apart again. The bios is already set to x16 which was required to get the graphics card to run at x16 since I don't have a gen 5 SSD.

 

[Maxxify]

Can keep an eye on link speed with CrystalDiskInfo. A UEFI reset might reconfigure it right. However, I've seen plenty of issues with M.2 on this chipset. The M.2_1 comes from the PCH/chipset in x16 mode (for GPU) or will bifurcate x8/x8 up to the link speed of the discrete GPU (e.g., 8x/8x at 4.0). You would lose 1-3% FPS with a 4090 (TPU and GN have tested this) with x8/x8 but you could see if the drive runs at x4 4.0 in that mode to verify the slot. FYI, a Gen5 SSD won't run at 5.0 unless the GPU is 5.0 (none out yet).

 

[mikeyymonster]

Can keep an eye on link speed with CrystalDiskInfo. A UEFI reset might reconfigure it right. However, I've seen plenty of issues with M.2 on this chipset. The M.2_1 comes from the PCH/chipset in x16 mode (for GPU) or will bifurcate x8/x8 up to the link speed of the discrete GPU (e.g., 8x/8x at 4.0). You would lose 1-3% FPS with a 4090 (TPU and GN have tested this) with x8/x8 but you could see if the drive runs at x4 4.0 in that mode to verify the slot. FYI, a Gen5 SSD won't run at 5.0 unless the GPU is 5.0 (none out yet). The nature of that connection makes a lot of trouble for M.2 on any of these boards.

I actually just tried resetting the CMOS to see if any changes. The PCIE was configured back to auto mode and switched the 4090 to x8/x8, but the M.2 was still locked at x2. Since I'm well within my return window, I am going to try replacing the mobo to rule that out.

Will report back if/any changes. If not, I will probably just leave it. In the event 1 of the drives is going to be stuck at x2, I'm assuming I should leave my main 2TB OS drive in x4 and my 4TB backup/games drive in x2?

 

[Maxxify]

I actually just tried resetting the CMOS to see if any changes. The PCIE was configured back to auto mode and switched the 4090 to x8/x8, but the M.2 was still locked at x2. Since I'm well within my return window, I am going to try replacing the mobo to rule that out.

Will report back if/any changes. If not, I will probably just leave it. In the event 1 of the drives is going to be stuck at x2, I'm assuming I should leave my main 2TB OS drive in x4 and my 4TB backup/games drive in x2?

Roger. If it's x2 in both modes, it's either a UEFI issue (that might be patched in the future) or a slot issue. As I said, not terribly uncommon with Z790 (particularly I) in my experience. The CPU is providing the lanes in one case, the chipset in the other, but that doesn't rule out a compatibility issue with the board somewhere that might get fixed or work with an RMA. (especially if the connector is proprietary or pseudo-proprietary; it looks like maybe a 2C connector though)

x2 4.0 is not a big deal. You lose out on maximum bandwidth but you get all the other benefits. The actual TLC speed is easily below x2 4.0, too, for sustained operations. The drive will also operate more efficiently with an x2 link width. The 4TB 990 PRO has newer flash which appears to be mainly for capacity so either drive in either place, but I guess 4TB is better for the x4 M.2 given that you won't be using CPU lanes on the M.2_1 (CPU lanes have slightly better latency) since it has a larger capacity and SLC cache. Although, if the 2TB if for OS/apps and the 4TB for games, it's surely fine to use the 2TB at x4.

 

[mikeyymonster]

Roger. If it's x2 in both modes, it's either a UEFI issue (that might be patched in the future) or a slot issue. As I said, not terribly uncommon with Z790 (particularly I) in my experience. The CPU is providing the lanes in one case, the chipset in the other, but that doesn't rule out a compatibility issue with the board somewhere that might get fixed or work with an RMA. (especially if the connector is proprietary or pseudo-proprietary; it looks like maybe a 2C connector though)

x2 4.0 is not a big deal. You lose out on maximum bandwidth but you get all the other benefits. The actual TLC speed is easily below x2 4.0, too, for sustained operations. The drive will also operate more efficiently with an x2 link width. The 4TB 990 PRO has newer flash which appears to be mainly for capacity so either drive in either place, but I guess 4TB is better for the x4 M.2 given that you won't be using CPU lanes on the M.2_1 (CPU lanes have slightly better latency) since it has a larger capacity and SLC cache. Although, if the 2TB if for OS/apps and the 4TB for games, it's surely fine to use the 2TB at x4.

I just want to report back that replacing the motherboard has resolved the issue. Thanks again for your help. I'm a bit bummed that I wasted all that time troubleshooting, but glad I got to the bottom of it!

On a side note, is it necessary do another clean install of windows due to the change of motherboard even if it's the exact same board?

 

[thestryker]

On a side note, is it necessary do another clean install of windows due to the change of motherboard even if it's the exact same board?

nope

 

[Maxxify]

I just want to report back that replacing the motherboard has resolved the issue. Thanks again for your help. I'm a bit bummed that I wasted all that time troubleshooting, but glad I got to the bottom of it!

Good to know. I actually shared your situation on my discord yesterday and there was a bit of discussion on it given the layout, but generally it was agreed that if it's x2 in both modes then it's the slot/board/connector. So it's good to have confirmation of that.