[SOLVED] PCIE lanes for Nvme Pcie m.2

Gabe666

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Jan 25, 2017
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Hello everyone!
I am a big noob regarding modern storage and I want to keep it short and simple so I am asking directly:
-ROG Crosshair VIII Hero https://www.asus.com/Motherboards/ROG-Crosshair-VIII-Hero/specifications/
-R9 3900x Cpu
-planing to buy 3080ti (or the rumored 3090 if under 1500$) which will 100% sure be a 16x pcie 4.0 Gpu (even if it turns out to still be pcie3.0, it's better to plan for the ''worst case'' for my pcie lanes).
Because I found contradicting information on this topic, it is unclear to me if:
1) will installing a nvme 4x pcie 3.0 m.2 SSD make the expensive GPU (or CPU??) any slower (even 1-2%)?
There would be only 1 nvme ssd.. all the rest storage are SATA.
  1. using a 4x pcie 3.0 ssd, will I lose 4x 4.0 lanes anyway? (so it would make more sense\better use of the lanes to buy the new pcie 4.0 ssd?).
  2. is it better for the m.2 pcie nvme ssd to run on the cpu pcie lanes or on the chipset (motherboard) pcie lanes? (I understand that my motherboard has some extra pcie lanes from chipset). Can I even decide\change on which lanes the ssd will run?
  3. I have my eyes on the Samsung 970 and wanted to get the PRO but then I saw that the cheaper Evo is faster (IOPS and write speed).
How can this be? In this case, the shorter lifespan of the evo is worth it. I will probably go for 1tb evo plus than the planned 512gb PRO
https://www.samsung.com/us/computing/memory-storage/solid-state-drives/ssd-970-evo-plus-nvme-m-2-1-tb-mz-v7s1t0b-am/#specs
https://www.samsung.com/us/computing/memory-storage/solid-state-drives/ssd-970-pro-nvme-m2-512gb-mz-v7p512bw/#specs

P.S: will I need a heatsink on this pcie ssd if I only use it for gaming( 90% of the time only read operation)?

Thank you all in advance!
 
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Maxxify

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The primary M.2 socket (M.2_1) uses dedicated CPU lanes so won't interfere with anything directly. The secondary M.2 socket (M.2_2) is over the chipset which won't interfere with the GPU's dedicated CPU lanes. M.2_1 is ideal since you'll have less latency by avoiding the chipset (which is basically a PCIe switch - it changes x4 PCIe 4.0 CPU lanes into x16 PCIe 4.0 virtual chipset lanes). The GPU PCIe slots have their own x16 CPU lanes, the only way to "lose" them would be to run two GPUs or something else in the 2nd main PCIe slot. Although if the 3080 Ti is PCIe 4.0-based it's likely x8 PCIe 4.0 lanes would not bottleneck it in real world gaming.

The 970 Pro is a prosumer drive using 2-bit MLC while the 970 EVO Plus is using 3-bit MLC (TLC) and is more consumer-leaning. This is because TLC-based drives will have a single-bit/SLC mode that's actually faster than MLC and most consumer workloads will fit inside this cache. I consider the 970 EVO Plus to be the best consumer drive on the market but it also tends to be overpriced for everyday use. There are many alternatives today. NVMe drives and the 970 EVO Plus specifically can run hot but it depends on your case/cooling. Your motherboard comes with built-in M.2 heatsinks though so it's a moot point.

As for "losing" lanes, lanes are lanes, so yes you are leaving potential bandwidth on the table by using a PCIe 3.0-based SSD in a PCIe 4.0-capable M.2 socket. However it's really only a factor for sequential performance which is not that important especially if you are only utilizing one drive.
 
Last edited:

Maxxify

Distinguished
The primary M.2 socket (M.2_1) uses dedicated CPU lanes so won't interfere with anything directly. The secondary M.2 socket (M.2_2) is over the chipset which won't interfere with the GPU's dedicated CPU lanes. M.2_1 is ideal since you'll have less latency by avoiding the chipset (which is basically a PCIe switch - it changes x4 PCIe 4.0 CPU lanes into x16 PCIe 4.0 virtual chipset lanes). The GPU PCIe slots have their own x16 CPU lanes, the only way to "lose" them would be to run two GPUs or something else in the 2nd main PCIe slot. Although if the 3080 Ti is PCIe 4.0-based it's likely x8 PCIe 4.0 lanes would not bottleneck it in real world gaming.

The 970 Pro is a prosumer drive using 2-bit MLC while the 970 EVO Plus is using 3-bit MLC (TLC) and is more consumer-leaning. This is because TLC-based drives will have a single-bit/SLC mode that's actually faster than MLC and most consumer workloads will fit inside this cache. I consider the 970 EVO Plus to be the best consumer drive on the market but it also tends to be overpriced for everyday use. There are many alternatives today. NVMe drives and the 970 EVO Plus specifically can run hot but it depends on your case/cooling. Your motherboard comes with built-in M.2 heatsinks though so it's a moot point.

As for "losing" lanes, lanes are lanes, so yes you are leaving potential bandwidth on the table by using a PCIe 3.0-based SSD in a PCIe 4.0-capable M.2 socket. However it's really only a factor for sequential performance which is not that important especially if you are only utilizing one drive.
 
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