Asus X870 motherboards - M2 slot selection

[MarkRich912]

Just a question for anyone who knows best regarding the proper selection of M2 slots for storage when there are shared PCIE lanes.
The Asus x870 boards have four M2 slots, two at PCIE 5x4 and two at PCIE 4x4. The first (M.2_1) is a full PCIE 5x4 with no shared lanes but after that I am hoping someone on here has a better understanding of this than I do.
M.2_2 is the second PCIE 5x4 slot but it shares lanes with the PCIE 5x16 which I'm assuming is the lanes that are intended for the dedicated GPU (assuming you put it in the obvious slot).
M.2_3 is a PCIE 4x4 but doesn't seem to share any lanes with either of the two full PCIE slots.
M.2_4 is a PCIE 4x4 that shares (or rather takes over) the lanes from the second PCIE slot.

My question then is, if you're fitting a second SSD onto this motherboard, assuming you have one in M.2_1 already, is it better to stick it in M.2_2 which is a higher gen PCIE but drops the PCIE5 slot to x8, or to stick it in M.2_3 which doesn't seem to conflict with anything but is only 4x4. Using M.2_4 would be equivalent to M.2_3 if there's no expansion card in the second PCIE slot (the gen4).

All theoretical, but my knowledge of PCIE lane sharing and the implications is basic at best.

 

[BlessedSquirrel]

Just a question for anyone who knows best regarding the proper selection of M2 slots for storage when there are shared PCIE lanes.
The Asus x870 boards have four M2 slots, two at PCIE 5x4 and two at PCIE 4x4. The first (M.2_1) is a full PCIE 5x4 with no shared lanes but after that I am hoping someone on here has a better understanding of this than I do.
M.2_2 is the second PCIE 5x4 slot but it shares lanes with the PCIE 5x16 which I'm assuming is the lanes that are intended for the dedicated GPU (assuming you put it in the obvious slot).
M.2_3 is a PCIE 4x4 but doesn't seem to share any lanes with either of the two full PCIE slots.
M.2_4 is a PCIE 4x4 that shares (or rather takes over) the lanes from the second PCIE slot.

My question then is, if you're fitting a second SSD onto this motherboard, assuming you have one in M.2_1 already, is it better to stick it in M.2_2 which is a higher gen PCIE but drops the PCIE5 slot to x8, or to stick it in M.2_3 which doesn't seem to conflict with anything but is only 4x4. Using M.2_4 would be equivalent to M.2_3 if there's no expansion card in the second PCIE slot (the gen4).

All theoretical, but my knowledge of PCIE lane sharing and the implications is basic at best.

You haven't said which motherboard as this wouldn't be the case over any Asus X870 motherboard, only the more budget options.

I take it this is about a motherboard for a PCSpecialist system? If you post the full specs you're proposing then we can offer better advice as all components interrelate

 

[MarkRich912]

Motherboard: Asus TUF x870 plus wifi
CPU: Ryzen 9 7950X
GPU: Asus TUF 4070 Super OC

At build there'll just be a single SSD in it, which I'm guessing they'll put in the M.2_1 position as that makes the most sense. I'm just wondering where a second SSD would best go if I did add one at a later date. The notes on the motherboard from Asus state that M.2_2 shares lanes with the G5 PCIE slot, so sticking a second SSD in that slot nerfs the GPU lanes. Using M.2_4 disables the G4 PCIE slot entirely , but M.2_3 has no such advisories.

Like I said, all academic at this point as I'm not planning any immediate upgrades, just curious as this is the first time I've dealt with on-mobo storage rather than SATA (and I'm dating myself horribly there).

 

[BlessedSquirrel]

Motherboard: Asus TUF x870 plus wifi
CPU: Ryzen 9 7950X
GPU: Asus TUF 4070 Super OC

At build there'll just be a single SSD in it, which I'm guessing they'll put in the M.2_1 position as that makes the most sense. I'm just wondering where a second SSD would best go if I did add one at a later date. The notes on the motherboard from Asus state that M.2_2 shares lanes with the G5 PCIE slot, so sticking a second SSD in that slot nerfs the GPU lanes. Using M.2_4 disables the G4 PCIE slot entirely , but M.2_3 has no such advisories.

Like I said, all academic at this point as I'm not planning any immediate upgrades, just curious as this is the first time I've dealt with on-mobo storage rather than SATA (and I'm dating myself horribly there).

Is this a specialist’s system? Can you post the full specs from the order page?

 

[MarkRich912]

Not a specialist build. Given the PC it's replacing is about 7 years old it'll run everything that did with ease, but it'll allow for some games etc that were out of reach of a 1060.

Case: CORSAIR 4000D RGB AIRFLOW TEMPERED GLASS GAMING CASE
Processor (CPU): AMD Ryzen 9 7950X 16 Core CPU (4.5GHz-5.7GHz/80MB CACHE/AM5)
Motherboard: ASUS® TUF GAMING X870-PLUS WIFI (AM5, DDR5, M.2 PCIe 5.0, Wi-Fi 7)
Memory (RAM): 32GB Corsair VENGEANCE DDR5 6000MHz (2 x 16GB)
Graphics Card: 12GB ASUS TUF GEFORCE RTX 4070 SUPER OC EDITION - HDMI, 3 x DP
1st M.2 SSD Drive: 2TB SOLIDIGM P44 PRO GEN 4 M.2 NVMe PCIe SSD (up to 7000MB/sR, 6500MB/sW)
Power Supply: CORSAIR 850W RMx SERIES™ MODULAR 80 PLUS® GOLD, ULTRA QUIET
Processor Cooling: PCS FrostFlow 360 Series ARGB High Performance Liquid Cooler
Thermal Paste: ARCTIC MX-4 EXTREME THERMAL CONDUCTIVITY COMPOUND
Extra Case Fans: 1 x 120mm Thermaltake TOUGHFAN 12 Case Fan
Sound Card: ONBOARD 6 CHANNEL (5.1) HIGH DEF AUDIO (AS STANDARD)
Network Card: ONBOARD 2.5Gbe LAN PORT
Wireless Network Card: NONE OR ONBOARD Wi-Fi (MOTHERBOARD DEPENDENT)
USB/Thunderbolt Options: 2 PORT (1 x TYPE A, 1 x TYPE C) USB 3.1 PCI-E CARD + STANDARD USB PORTS

 

[BlessedSquirrel]

Not a specialist build. Given the PC it's replacing is about 7 years old it'll run everything that did with ease, but it'll allow for some games etc that were out of reach of a 1060.

Case: CORSAIR 4000D RGB AIRFLOW TEMPERED GLASS GAMING CASE
Processor (CPU): AMD Ryzen 9 7950X 16 Core CPU (4.5GHz-5.7GHz/80MB CACHE/AM5)
Motherboard: ASUS® TUF GAMING X870-PLUS WIFI (AM5, DDR5, M.2 PCIe 5.0, Wi-Fi 7)
Memory (RAM): 32GB Corsair VENGEANCE DDR5 6000MHz (2 x 16GB)
Graphics Card: 12GB ASUS TUF GEFORCE RTX 4070 SUPER OC EDITION - HDMI, 3 x DP
1st M.2 SSD Drive: 2TB SOLIDIGM P44 PRO GEN 4 M.2 NVMe PCIe SSD (up to 7000MB/sR, 6500MB/sW)
Power Supply: CORSAIR 850W RMx SERIES™ MODULAR 80 PLUS® GOLD, ULTRA QUIET
Processor Cooling: PCS FrostFlow 360 Series ARGB High Performance Liquid Cooler
Thermal Paste: ARCTIC MX-4 EXTREME THERMAL CONDUCTIVITY COMPOUND
Extra Case Fans: 1 x 120mm Thermaltake TOUGHFAN 12 Case Fan
Sound Card: ONBOARD 6 CHANNEL (5.1) HIGH DEF AUDIO (AS STANDARD)
Network Card: ONBOARD 2.5Gbe LAN PORT
Wireless Network Card: NONE OR ONBOARD Wi-Fi (MOTHERBOARD DEPENDENT)
USB/Thunderbolt Options: 2 PORT (1 x TYPE A, 1 x TYPE C) USB 3.1 PCI-E CARD + STANDARD USB PORTS

So I'm afraid we can't comment if it's not a PCSpecialist system, you'd need to find an open forum to advise.

 

[TonyCarter]

Are we confusing a 'PC Specialist' build, or just 'a specialist' build, as that config has PCS AIO in, which isn't available from anywhere else.

 

[MarkRich912]

My bad. It is a PCS build. It's not a "specialist" build in terms of intended use, as I misinterpreted.

 

[TonyCarter]

You are correct in the reading of the m2 slot speeds.

A PCIe 5.0x4 will be 2x faster than a 4.0x4 - it's just the GPU slot that will be reduced to 5.0x8. If you have a SSD with lower than 16,000MB/s (i.e. Gen3/4) then you won’t saturate the PCIe 5.0x4 m2_2 slot. I don’t think there are any gen5 SSDs that are above 12,000MB/s currently…and fast gen 5 ones are not cheap.

But it would only be an issue if you got hold of a GPU that could saturate the PCIe 5x16 slot…a current RTX4090 only just saturates a PCIe 3.0x16 slot, so PCIe 5.0x8 (same as 4.0x16) will have plenty of headroom for a few top-end GPU revision.

 

[MarkRich912]

You are correct in the reading of the m2 slot speeds.

A PCIe 5.0x4 will be 2x faster than a 4.0x4 - it's just the GPU slot that will be reduced to 5.0x8. If you have a SSD with lower than 16,000MB/s (i.e. Gen3/4) then you won’t saturate the PCIe 5.0x4 m2_2 slot. I don’t think there are any gen5 SSDs that are above 12,000MB/s currently…and fast gen 5 ones are not cheap.

But it would only be an issue if you got hold of a GPU that could saturate the PCIe 5x16 slot…a current RTX4090 only just saturates a PCIe 3.0x16 slot, so PCIe 5.0x8 (same as 4.0x16) will have plenty of headroom for a few top-end GPU revision.

Awesome thanks for the info. Nice to know there's plenty of room for future upgrades on the board!