I recently built my PC with a Ryzen 5 3600, an Asus PRIME B450-PLUS motherboard, and an RTX 2070 Super GPU. Currently, I have one M.2 SSD installed in the standard M.2 slot. To expand my storage, I purchased a PCIe to 4x M.2 adapter card since I have a free x16 slot (with the other occupied by my GPU). The first SSD was detected without issues, but my second SSD isn't recognized. I've come across terms like PCIe lanes and PCIe bifurcation but need clarification on these concepts. My goal is to use the second SSD for dual-booting Windows and Linux. Can someone explain why my second SSD isn't working, and what options I have? Should I consider getting a new motherboard or using a different setup?
3 Answers
Each M.2 SSD uses four PCIe lanes, and in your case, the PCIEX16_2 slot is only capable of supporting four lanes (the design confirms that with fewer metal contacts). If you want to add storage, consider an adapter that goes from M.2 to SATA or PCIe x1, which will slow down the performance but offer more options than what you're currently facing.
Your best options might be to look for a motherboard that has more native M.2 slots, or drive prices may come down enough for you to choose SATA drives instead if you're okay with that decrease in speed.
The x16 slot you mentioned might look large enough, but it's only wired for x4 operation because of your motherboard's design. This means you can't connect more than one M.2 drive in that slot. So, it's not about the adapter but about the constraints set by your motherboard.
To dig deeper into this, check your motherboard's manual for lane allocation. You may want to look for diagrams or specs that explain PCIe configurations. Upgrading to a new motherboard that supports bifurcation could solve this, or you could even consider splitting your SSD usage by partitioning the first drive, but that might not be ideal for your plans.
You've got the right idea with PCIe bifurcation – it lets a motherboard treat a single x16 slot as multiple smaller slots (like x4 slots). However, not all motherboards, including yours, support bifurcation across all slots. The actual wiring matters too; even if a slot looks like it can fit an x16 card, it might only function as x4.
Your current choices are limited: you could invest in a better motherboard that has more native M.2 slots or PCIe support, or look for PCIe adapter cards that include bifurcation chips... although these can get pricey. If just connecting different operating systems is your goal, think about creating partitions instead of buying new hardware for the second SSD.
If I do go with another motherboard, what should I look for specifically regarding PCIe support? Should I prioritize how many M.2 slots it has, or focus more on bifurcation capabilities?
Thanks for the info! Just to clarify – is this limitation strictly due to the motherboard's design, or could the CPU also play a role in how many lanes each slot supports?