For stuff like PCIe and SATA, M.2 typically keeps all high-speed diffpairs on the card’s top side, and this alone helps a bunch with aspects like an uninterrupted ground layer under your pairs.
The IntelliProp IPP-SA128A-PM (SATA Port Multiplier with Sandbox) device is an IP core that provides SATA Port Multiplier functionality with support for up to 15 SATA storage devices. The IP core is ...