In my limited real world testing with the ASUS H170-PLUS D3 (2 SATA ports routed to a single M.2), a drive attached to the second port was not visible in BIOS menus, but it was still initialized by ...

Although SATA drives can be connected to a SAS interface ... with two full-duplex channels that operate simultaneously. Each channel (SAS port) transfers data at 3, 6 or 12 Gbps in each direction.

Maximum supported bandwidth is 48 Gbps. The serial link employs multiple high-speed gigabit transceivers. Automatically detects SAS and SATA drives.

Improves performance for storage intensive workloads such as databases and sets new speed and data security standards for internal storage drives Supports up to 256 SAS/SATA HDDs and SSDs, 4 NVMe SSDs ...