I recently moved my FreeNAS server to a larger case featuring the SuperMicro SAS2-837EL2 SAS backplane with dual expanders and wanted to validate my configuration. I have a single LSI-2308 based HBA in the server and I ran a SFF-8087 cable from each port of the HBA to the incoming port on each of the expanders thinking this would allow me to take advantage of the second path in case of hardware failure. Probably gross overkill for my needs but why the heck not. Everything came back OK but...
FreeNAS with dual expander backplane
FreeNAS with dual expander backplane