Before anything else this projects requires experience in working with High Speed Interfaces(PCIE Gen3 or more) and ASMEDIA IC (PCIE switches, SATA Bridges etc, you will need reference design for these IC).
This task involves designing a server backplane: schematic + board layout + BOM + GERBER.
The board is to be built around a PCIE switch (like ASMedia ASM2812 for i.e.) and a SATA controller ( ASMedia ASM1166 for i.e.) with upstream: PCIe Gen3 and downstream: SATA + M.2 M-key connector downstream + LEDs and Fans outputs.
Please check the attached basic schematic:
- The configuration would use an M.2 extension adapter card to transfer the 4x PCIe lanes to the backplane via a 20cm Flex-PCB or another cost effective alternative solution (i.e. SFF-8543 connectors and cables).
The switch is needed on the backplane because the server board has no support for PCIE lanes splitting.
So while the M-Key M.2 card connects to 4 lanes the SATA bridge IC needs only 2 of them. So to avoid wasting 2 lanes a PCIE switch is used to route 2 lanes to the SATA bridge and also switch all the 4 lanes to another M-Key M.2 connector that will permit a NVME card to be attached to the backplane.
That's the basics.
Time to completion is set to be flexible so no issue here.
The complete documentation will follow.
Hope to hear from you. Thanks. HW