8i/16i RAID/HBA adapter + retimer card
The following shows the cable connections for the 8 x 2.5-inch SAS/SATA + 8 x 2.5-inch NVMe configuration 
with one 8i/16i RAID/HBA adapter and one retimer card.
From To
Backplane 1: SAS 8i/16i* RAID/HBA adapter on PCIe slot 2:
•  Gen 3: C0C1
•  Gen 4: C0
Backplane 2: NVMe 0-1, 2-3
Onboard: PCIe 1, PCIe 2
Backplane 2: NVMe 4-5, 6-7
Retimer card on PCIe slot 1: C0, C1
Note: *If a 16i RAID adapter is used, SAS cable 
1  has an extra dummy connector (not shown in below 
illustration) to connect to the other connector of the 16i RAID adapter.
Connections between connectors: 
1  ↔  1 ,  2  ↔  2 ,  3  ↔  3 , ...  n  ↔  n
Figure 66. SAS/SATA cable routing
Figure 67. NVMe cable routing
120 ThinkSystem SR650 V2Maintenance Manual