Nvme vs PCIE

The number of NVMe disks a PCIe 4.0 slot can support at full speed depends on how many PCIe lanes are available on the slot and how the NVMe SSDs are connected through the adapter.

PCIe 4.0 Bandwidth and Lane Configuration:

• PCIe 4.0 can deliver 16 GT/s (Gigatransfers per second) per lane, and each lane provides a theoretical 2 GB/s of bandwidth in each direction.

• Typically, a single NVMe SSD requires 4 PCIe lanes (x4) to operate at full speed, which provides a maximum theoretical throughput of 8 GB/s (since PCIe 4.0 x4 offers around 8 GB/s in total bandwidth).

Scenarios for Multiple NVMe Drives:

1. Single PCIe 4.0 x16 Slot:

• A PCIe 4.0 x16 slot can provide 16 lanes of bandwidth. If you’re using a PCIe to NVMe adapter that supports multiple drives, the number of NVMe disks it can fully support depends on how it splits the bandwidth across the lanes.

• Example: A PCIe 4.0 x16 slot theoretically supports 4 NVMe drives in a 4×4 configuration (one x4 for each drive), delivering full-speed performance (up to 8 GB/s per SSD).

2. Single PCIe 4.0 x8 Slot:

• A PCIe 4.0 x8 slot provides 8 lanes, so it can support 2 NVMe SSDs at full speed (each getting 4 lanes or x4).

3. Single PCIe 4.0 x4 Slot:

• A PCIe 4.0 x4 slot provides 4 lanes, which means it can support 1 NVMe SSD at full speed.

4. PCIe 4.0 x1 Slot:

• A PCIe 4.0 x1 slot provides just 1 lane, which can support only one NVMe SSD at a much slower speed (lower than the typical x4 configuration for NVMe).

Conclusion:

• A PCIe 4.0 x16 slot can fully support up to 4 NVMe drives at full speed (if the adapter is designed for this).

• A PCIe 4.0 x8 slot can support 2 NVMe drives at full speed.

• A PCIe 4.0 x4 slot can support 1 NVMe drive at full speed.

So, to maximize the number of NVMe SSDs running at full speed, you need to ensure you have a PCIe 4.0 x16 slot and a multi-drive NVMe adapter capable of splitting the lanes correctly.