Use all m2 slots on motherboard?

[patseguin Global Moderator]

I have my new build with a 13700K i7 and an ASUS z790 motherboard which has 5 m2 slots. When I first did the build, I only used 2, but then the Samsung 2TB 980’s were at such a good price that I filled the rest. Is there anything wrong with that? Someone told me to make sure my system has enough pcie lanes to handle that, but why would the board have 5 slots if you’re not meant to use them? The system is running fine, but my 4080 GPU isn’t taking a performance hit, is it?

[ThePhoenix]

If you check the mobo manual it'll identify which components will be affected by your use of which slots.  Usually either sacraficing SATA Ports or in some cases PCIE Slots for expansion cards.

That will show which slot affects what and what speed impact it will have depending on if use NVMe or mSATA etc.

[sagum]

Generally your motherboard has two ways to connect devices to the CPU's PCI bus.

The first is direct. This is usually slot 1 on the motherboard and you'll want to use your GPU for this.
Then you usually have at least one m.2 slot that is directly connected to the CPU, beware that this also usually shares the same PCI lanes as the GPU. So a x16 GPU slot can be reduced to a x8 slot if some are used by the m.2 drive installed.

With the CPU having limited in PCI lanes, the remaining slots be it m.2 or PCI will usually be connected to the motherboard chipset, and then chipset connected to the CPU lanes.
The chipset allows multiple devices to share the PCI lanes that are left, but at the cost of some of them running slower if the bandwidth is being used.

On higher end boards, or ones that support CPUs with a lot of CPU lanes, you may have multiple PCI/m.2 slots that are directly connected to the CPU and they might all run at full speed.

You'll need to consult your motherboard manual for specs and determine if the board's GPU PCI slot is effected by having the primary m.2 slot filled.
Given that most 13th gen intel CPU are 20 lane, I'm going to assume it's probably the case.
 

If you don't notice any performance issues with the GPU and having the m.2 installed, don't worry about it. If you do, then you and have PCI slots free you might want to move it to a PCI m.2 expansion card to free up the GPU's lanes.

 

 

[Jim K Global Moderator]

Yea...check the manual.  Assuming you have a Strix Z790....

 

Quote

When M.2_1 is occupied with SSD device, PCIEX16(G5) will run x8 only.

https://dlcdnets.asus.com/pub/ASUS/mb/LGA1700/ROG_STRIX_Z790-E_GAMING_WIFI/E20593_ROG_STRIX_Z790-E_GAMING_WIFI_UM_WEB.pdf?model=ROG STRIX Z790-E GAMING WIFI

[patseguin Global Moderator]

On 26/03/2023 at 10:59, sagum said:

Generally your motherboard has two ways to connect devices to the CPU's PCI bus.

The first is direct. This is usually slot 1 on the motherboard and you'll want to use your GPU for this.
Then you usually have at least one m.2 slot that is directly connected to the CPU, beware that this also usually shares the same PCI lanes as the GPU. So a x16 GPU slot can be reduced to a x8 slot if some are used by the m.2 drive installed.

With the CPU having limited in PCI lanes, the remaining slots be it m.2 or PCI will usually be connected to the motherboard chipset, and then chipset connected to the CPU lanes.
The chipset allows multiple devices to share the PCI lanes that are left, but at the cost of some of them running slower if the bandwidth is being used.

On higher end boards, or ones that support CPUs with a lot of CPU lanes, you may have multiple PCI/m.2 slots that are directly connected to the CPU and they might all run at full speed.

You'll need to consult your motherboard manual for specs and determine if the board's GPU PCI slot is effected by having the primary m.2 slot filled.
Given that most 13th gen intel CPU are 20 lane, I'm going to assume it's probably the case.
 

If you don't notice any performance issues with the GPU and having the m.2 installed, don't worry about it. If you do, then you and have PCI slots free you might want to move it to a PCI m.2 expansion card to free up the GPU's lanes.

 

Jeez I’ve been building since like 1992 and I have to catch up on technology. I have the ASUS ROG Strix z790-E gaming. I just looked through the manual and couldn’t find anything about limitations of using the 5 m2 slots, just installing in them. Here’s a diagram…

[sagum]

On 26/03/2023 at 16:49, patseguin said:

Jeez I’ve been building since like 1992 and I have to catch up on technology. I have the ASUS ROG Strix z790-E gaming. I just looked through the manual and couldn’t find anything about limitations of using the 5 m2 slots, just installing in them. Here’s a diagram…

 

I checked your motherboard manual, ROG STRIX Z790-E GAMING WIFI Specifications Summary page vii , under Expansion Slots it says 
 

** When M.2_1 is occupied with SSD device, PCIEX16(G5) will run x8 only.

https://dlcdnets.asus.com/pub/ASUS/mb/LGA1700/ROG_STRIX_Z790-E_GAMING_WIFI/E20593_ROG_STRIX_Z790-E_GAMING_WIFI_UM_WEB.pdf

 

[patseguin Global Moderator]

On 26/03/2023 at 12:13, sagum said:

 

I checked your motherboard manual, ROG STRIX Z790-E GAMING WIFI Specifications Summary page vii , under Expansion Slots it says 
 

** When M.2_1 is occupied with SSD device, PCIEX16(G5) will run x8 only.

https://dlcdnets.asus.com/pub/ASUS/mb/LGA1700/ROG_STRIX_Z790-E_GAMING_WIFI/E20593_ROG_STRIX_Z790-E_GAMING_WIFI_UM_WEB.pdf

 

Well, that stinks. You’d think with it being the #1 slot it would be the main one intended to use. That’s the one I used since I completed my build. That means my 4080 has been running on x8 this whole time. Have I been take a big performance hit this whole time?

 

edit: it’s a pain to get to the m2 slots because I have to remove my 4080 and vertical stabilizer. However, would a good solution be to move that drive to another m2 slot since it’s my boot drive and take an m2 and put it on some kind of card that goes into a pcie slot?

[+Matthew S. Subscriber²]

You shouldn't really notice any performance loss unless your pushing that GPU to its limit.

[patseguin Global Moderator]

On 27/03/2023 at 03:01, Matthew S. said:

You shouldn't really notice any performance loss unless your pushing that GPU to its limit.

Yeah I asked in the Geforce forums and they said the same. I'd only notice in extreme 3D rendering, not in gaming. Still though, I figured out that in fact I only populated 4 of the 5 m2 slots. Now I need to decide if it's worth the hassle of opening it up and taking out the brace and graphics card and move it (peeling off the thermal pad).

[goretsky Supervisor]

Hello,

I would suggest the following:

1.  Remove all five of the Samsung 980 2 TB M.2 2280 NVMe SSDs from their respective slots (labeled M2_1 … M2_5, respectively, on the motherboard), one at a time, clearly labeling each one as #1-5 (or otherwise keeping track of which NVMe SSD was in each M.2 slot).
2. Insert the original Samsung 980 2 TB M.2 2280 NVMe SSD boot drive from the M2_1 slot into the M2_2, which is the PCIe 4.0 ×4 slot that interfaces directly with the processor.
3. Power up the computer as you normally do, and verify the computer boots up correctly into Microsoft Windows.  If it does not, enter the BIOS (UEFI) firmware and make whatever changes are necessary in order for the drive to be detected as the primary boot device, and boot into Windows.
4. Perform an immediate power down after booting successfully into Windows  (use a "SHUTDOWN /P" command from an elevated Command Prompt (filename: CMD.EXE) to avoid Modern Standby/sleep/low power conservation modes.
5. In order, install the next three Samsung 980 2 TB M.2 2280 NVMe SSDs (previously labeled as #2 through #4) into the M.2 slots labeled as M2_3 though M2_5.
6. Lastly, install the last Samsung 980 2 TB M.2 2280 NVMe SSD (previously labeled as #5) into an NVMe to PCIe 4.0 ×4 card adapter.  Here are examples of adapters which are marketed as PCIe 4.0 compliant: Icy Dock and Micro Connectors.  I will note that these appear to be passive ("dumb") adapters without any components on them, so it is possible a PCIe 3.0 ×4 will work equally well in a PCIe 4.0 slot. 
7. Insert the assembled card into one of the PCIe 4.0 slots available on the motherboard, labeled as PCIEX16(G4)_1 or PCIEX16(G4)_2.  While these slots have full-length ×16 connectors, each one is only wired electrically as a ×4 to the motherboard's Z790 chipset, so it is of no benefit to use an PCIe ×8 or ×16 card in either slot.

After this is done, reassemble the computer and verify the drives are properly recognized by the operating system.

Another option, if you do not want to mount any of the Samsung 980 2 TB M.2 2280 NVMe SSDs back into the motherboard is to get a PCIe ×4 to quad port NVMe adapter.  I found this model on Newegg: Yucheng PCIE 3.0 ×4 PLX8724 to 4-Port M.2 NVMe SSD Adapter Card.  That is a PCIe 3.0 card, so it will only operate at half the speed of PCIe 4.0 slot; I could not find a PCIe 4.0 version, although it is possible the vendor has one for sale elsewhere.  That should make for a more portable solution, should you wish to transfer the drives to another system, or upgrade to higher capacity drives in the future.

Regards,

Aryeh Goretsky
 

[patseguin Global Moderator]

On 28/03/2023 at 02:14, goretsky said:

Hello,

I would suggest the following:

1.  Remove all five of the Samsung 980 2 TB M.2 2280 NVMe SSDs from their respective slots (labeled M2_1 … M2_5, respectively, on the motherboard), one at a time, clearly labeling each one as #1-5 (or otherwise keeping track of which NVMe SSD was in each M.2 slot).
2. Insert the original Samsung 980 2 TB M.2 2280 NVMe SSD boot drive from the M2_1 slot into the M2_2, which is the PCIe 4.0 ×4 slot that interfaces directly with the processor.
3. Power up the computer as you normally do, and verify the computer boots up correctly into Microsoft Windows.  If it does not, enter the BIOS (UEFI) firmware and make whatever changes are necessary in order for the drive to be detected as the primary boot device, and boot into Windows.
4. Perform an immediate power down after booting successfully into Windows  (use a "SHUTDOWN /P" command from an elevated Command Prompt (filename: CMD.EXE) to avoid Modern Standby/sleep/low power conservation modes.
5. In order, install the next three Samsung 980 2 TB M.2 2280 NVMe SSDs (previously labeled as #2 through #4) into the M.2 slots labeled as M2_3 though M2_5.
6. Lastly, install the last Samsung 980 2 TB M.2 2280 NVMe SSD (previously labeled as #5) into an NVMe to PCIe 4.0 ×4 card adapter.  Here are examples of adapters which are marketed as PCIe 4.0 compliant: Icy Dock and Micro Connectors.  I will note that these appear to be passive ("dumb") adapters without any components on them, so it is possible a PCIe 3.0 ×4 will work equally well in a PCIe 4.0 slot. 
7. Insert the assembled card into one of the PCIe 4.0 slots available on the motherboard, labeled as PCIEX16(G4)_1 or PCIEX16(G4)_2.  While these slots have full-length ×16 connectors, each one is only wired electrically as a ×4 to the motherboard's Z790 chipset, so it is of no benefit to use an PCIe ×8 or ×16 card in either slot.

After this is done, reassemble the computer and verify the drives are properly recognized by the operating system.

Another option, if you do not want to mount any of the Samsung 980 2 TB M.2 2280 NVMe SSDs back into the motherboard is to get a PCIe ×4 to quad port NVMe adapter.  I found this model on Newegg: Yucheng PCIE 3.0 ×4 PLX8724 to 4-Port M.2 NVMe SSD Adapter Card.  That is a PCIe 3.0 card, so it will only operate at half the speed of PCIe 4.0 slot; I could not find a PCIe 4.0 version, although it is possible the vendor has one for sale elsewhere.  That should make for a more portable solution, should you wish to transfer the drives to another system, or upgrade to higher capacity drives in the future.

Regards,

Aryeh Goretsky
 

Thanks but I'm not sure I need to go to those extents because everything is functioning properly. My only concern was limiting performance by using all of the m2 slots. As I found out, using the #1 m2 slot cuts the pciex16 slot to x8. I was thinking about moving it (because I figured out that I only have 4 m2's, I must have miscounted because I have a few regular SSD drives too) but my research tells me that I will not notice a difference in gaming, only high end rendering and really stressing the card. Still because of my OCD building systems, I might move it and open up x16 hehe.

[Steven P. Administrators]

On my Gigabyte Aorus Z390 Pro WiFi the two onboard NVMe share lanes with the SATA ports, so the PCIe card slots aren't affected. I checked because I have 3 NVMe (one is in a PCIe card) and a SATA connected 2TB 870 QVO 2.5" SSD, and I wanted to make sure they didn't interfere with each other.

When I eventually upgrade I am going to have to make a mental note to ensure NVMe aren't sharing PCIe lanes with any card slots, which seems like a dumb idea.