Rear backplane: 4 x 2.5-inch SAS/SATA
The following shows the cable connections for a rear 4 x 2.5-inch SAS/SATA backplane if installed.
From To
Backplane 4: SAS 8i RAID/HBA adapter on PCIe slot 6:
•  Gen 3: C0C1
•  Gen 4: C0
Backplane 4: PWR Riser 1: PWR1, PWR2
Connections between connectors:  1  ↔  1 ,  2  ↔  2 ,  3  ↔  3 , ...  n  ↔  n
Figure 100. Cable routing for the rear 2.5-inch SAS/SATA backplane
146 ThinkSystem SR650 V2Maintenance Manual