Patrick & Kal G, please help me understand this.
Patrick and others had reported that the R version worked in SOME Supermicro motherboards. Allegedly those that supported bifurcation by the motherboards BIOS and hardware. I believe Patrick confirmed that the more expensive non-R card was only needed sometimes, allegedly for motherboards without integrated bifurcation capability.
I assume that the Supermicro's Intel D motherboards are ones that have bifurcation. That is why Kal G's riser card's two x8 slots were seen as two separate devices. I believe he successfully used this for two RAID cards?
So if the Supermicro Intel D motherboard's bifurcation capability is like the ones Patrick, and others, tested to work with a single R card, then the motherboard successfully split a single motherboard slot into the two x4 gen 3 lanes needed by two connected Intel 750 NVMe SSDs? If the riser card simply provides two x8 slots, seen as two separate devices, by the motherboard's bifurcation, why would motherboard bifurcation not work for both riser supplied x8 slots, each populated with a R card?
Maybe the Supermicro motherboards that have bifurcation capability are limited to split a single x16 or x8 slot to two x4 slots, and cannot bifurcate two slots? I wonder if someone has the hardware in place to actually test the riser card, 2 R cards, and 4 Intel 750 NVMe 2.5 in SSDs? I guess the testing could be in steps.
First see if a R card with two Intel 750s works in the single x16 Supermicro Intel D motherboard without the riser card. Together with an M.2 adapter with provides a SFF-8643 mini-SAS HD connector, that would allow for a three NVMe SSD Raid-0 setup in a small footprint case.
Second plug a single R card into one of the riser card's x8 slots. Kal G says this will break the ability to use two Intel 750s, because the motherboard bifurcation capability 'has been used up' by the riser cards two x8 slots, and the riser card has no ability to use two sets of x4 lanes on one of its x8 slots, breaking the use of two Intel 750s.