Note: Gen 3 and Gen 4 SFF RAID/HBA adapters are slightly different in their connectors, but the connection 
method is similar. The following illustration takes Gen 4 SFF RAID/HBA adapters as an example.
Figure 192. Cable routing for 4 x 2.5'' AnyBay backplane drive with an 8i SFF RAID adapter (Gen 3 or Gen 4)
Table 33.  Mapping between one front AnyBay backplane and an SFF HBA/RAID adapter (Gen 3 or Gen 4)
From To
1  NVMe 0-1, NVMe 2-3 on the front backplane
1  PCIe connectors 3 and 4 on the system board 
assembly
2  SAS on the front backplane 2  C0 on the SFF HBA/RAID adapter
8 x 2.5'' front drives
Use the section to understand the cable routing for signal cable connections for 8 x 2.5'' front drive 
backplanes.
256 ThinkSystem SR635 V3 User Guide