16i HBA adatper + 8i RAID adapter
The following shows the cable connections for the 24 x 2.5-inch SAS/SATA configuration with one 16i HBA 
Gen 3 adapter and one 8i RAID Gen 3 adapter.
From To
Backplane 1: SAS 16i HBA adapter on PCIe slot 2: C0C1
Backplane 2: SAS 16i HBA adapter on PCIe slot 2: C2C3
Backplane 3: SAS 8i RAID adapter on PCIe slot 3: C0C1
Connections between connectors: 
1  ↔  1 ,  2  ↔  2 ,  3  ↔  3 , ...  n  ↔  n
Figure 45. Cable routing for the 24 x 2.5-inch SAS/SATA configuration with one 16i HBA adapter and one 8i RAID adapter
Chapter 3. Internal cable routing 101