Onboard connectors + 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 retimer card.
From To
Backplane 1: SAS Onboard: SATA 0, SATA 1
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
Connections between connectors: 
1  ↔  1 ,  2  ↔  2 ,  3  ↔  3 , ...  n  ↔  n
Figure 64. SAS/SATA cable routing
Figure 65. NVMe cable routing
Chapter 3. Internal cable routing 119