Front backplane: 24 x 2.5" SAS/SATA
This topic provides cable routing information for the front 24 x 2.5-inch SAS/SATA expander backplane.
8i adapter
Connections between connectors: 
1  ↔  1 ,  2  ↔  2 ,  3  ↔  3 , ...  n  ↔  n
Figure 467. Cable routing to 8i adapter
From To
1  Backplane 1: SAS 0
1  8i adapter 
•  Gen 4: C0
•  Gen 3: C0C1
Front + rear backplanes: 24 x 2.5" SAS/SATA + 4 x 2.5"/8 x 2.5" SAS/SATA/4 x 2.5" 
AnyBay
This topic provides cable routing information for the server model with one front 24 x 2.5-inch SAS/SATA 
expander backplane and one 4 x 2.5-inch/8 x 2.5-inch SAS/SATA/4 x 2.5-inch AnyBay rear backplane.
•  “24 x 2.5" SAS/SATA + 4 x 2.5" SAS/SATA” on page 433
•  “24 x 2.5" SAS/SATA + 4 x 2.5" AnyBay” on page 433
•  “24 x 2.5" SAS/SATA + 8 x 2.5" SAS/SATA” on page 434
432
ThinkSystem SR665 V3 User Guide