NVMe cable routing
From To
Backplane 3: NVMe 0-1, 2-3 Onboard: PCIe 1, PCIe 2
Backplane 3: NVMe 4-5, 6-7 Retimer card on PCIe slot 1: C0, C1
Connections between connectors: 
1  ↔  1 ,  2  ↔  2 ,  3  ↔  3 , ...  n  ↔  n
Figure 114. NVMe cable routing (one processor)
158 ThinkSystem SR650 V2Maintenance Manual