WD SN750 (500GB) in Mac Pro 5,1 speed issues

The Mac Pro has only 2.0 PCIe version and 16X and 4X slots.
In the 16X slot, the speed is around ~1400M/s but in the 4X slot just the half. The card and the drive are 4X. The speed should be the same. The firmware update didn’t help.

Hi @Esskaaell,

Please contact the WD Technical Support team for best assistance and troubleshooting:

Are you able to get details on the number of PCIe lanes being actively used by the SSD? Also which OS do you have installed on it?

For NVMe on older systems, many things can impact performance. On older chipsets from that time period, will often have at best 2GB/s of throughput between the chipset and CPU, and that throughput is shared with everything on the chipset, which will impact overall throughput for a chipset connected m.2 slot.

If the 4X slot is connected to the chipset, then you are likely sharing bandwidth with the SATA ports, USB ports, Ethernet controller, and various other components.

A slot with direct CPU PCIe lanes, will not need to share bandwidth, but there will still be overhead in how the the PCie signaling is handled, as well as how the motherboard handles the storage. For example, if the board or firmware will not allow a large enough payload size per frame, then it will limit performance.
The OS also plays an important role as NVMe drivers also impact performance.