Onboard connectors + onboard connectors
The following shows the cable connections for the 12 x 3.5-inch SAS/SATA configuration with a 2 x 3.5-inch 
SAS/SATA rear backplane.
From To
Backplane 1: SAS 0, SAS 1 Onboard: SATA 0, SATA 1
Backplane 1: SAS 2 Onboard: SATA 2
Backplane 4: SAS Onboard: Rear BP
Backplane 4: PWR Riser 1: PWR1, PWR2
Connections between connectors:  1  ↔  1 ,  2  ↔  2 ,  3  ↔  3 , ...  n  ↔  n
Figure 122. Front backplane cable routing Figure 123. Rear backplane cable routing
168 ThinkSystem SR650 V2Maintenance Manual