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Will a m.2 pcie adapter slow the read/write speed of the ssd?

HaichuanLi
  • 4 months ago

Hey guys, I was just wandering if the read/write speed of my ssd be reduced if I use a m.2 to pcie adapter. I'm planning to buy the msi b450 gaming pro carbon ac, but it says that if I plug an ssd to the second m.2 slot, the pcie 2,3,4 and 5 will be unavailable. Since I'm pretty sure that I'll get a second m.2 ssd later and that I still want to be able to use the other pcie slots, I'm planning to get an adapter that hopefully won't slow down the ssd's read/write speed. Thank you for you're time.

Comments

  • 4 months ago
  • 1 point

Well there are 2 types of M.2 PCIe cards. Sata based and NVMe based. They are very different as the Sata based ones needs a sata controller on the card and the NVMe one doesn't need a controller and just connects the PCIe lanes from the slot to the m.2 drive. As a result the simplicity of the NVMe PCIe expansion cards are cheaper.

As for speeds I don't really think there will be much penalty at all. Sata speeds cap out 560 MB/s and if you use a PCIe 4x card the slot can provide nearly 4GB/s so the bottleneck will be the SATA speed. Even if you have 4 SATA SSDs chugging away at the same time.

NVMe adaptors usually have 1 or 2 slots a card and a 2 slot card will run on PCIe x8 and provide 4 PCI lanes per NVMe drive. I have seen some adaptors where it only has a 4x slot and 2 NVMe SSDs and if you try to use the full speed on both that is when the slot becomes a bottleneck. For example 2x samsung 970 evo SSDs each reading at 3.5 GB/s that is a demand of 7GB/s. Now no home user is generally going to even do this but if it is bottlenecked on just a 4x slot then they will have to share ~4GB/s. To be honest outside data center loads I can't see very many things benefitting from that kind of SSD throughput.

If you get an 8x card and plug it into a 4x slot it is possible one NVMe slot on the expansion card may not work if the 4 PCIe lanes the card connects to is not even there. Check your motherboard manual about your PCIe slots and see what they run at.

  • 4 months ago
  • 1 point

B450 doesn't support splitting the graphics lanes so all secondary x16 slots are wired though the chipset at PCIe 2.0 speeds and will restrict the speeds of the SSD.

If you want to run multiple PCIe SSD you need to move to a X470 with SLI so you can use graphics lanes for PCIe adaptors or X570.

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