SM's current H11SSL-NC offers the LSI3008 RAID chip that supports up to 8 drives for your OS RAID. Their website only mentions "SAS" with the 3008 but I did inquire with SM's tech support with regards to SATA support and was informed it is supported and that 2 logical drives can be created (I generally build 1 or 2 RAID 10 drives of 4 disks each). I believe this is the only Rome MB of offering on-board RAID support. Although certainly not a requirement with the abundance of PCI-E slots available, one could easily add a RAID card of choice.
The other feature of the H11SSL-NC is the addition of 2 NVMe ports via mini-sas connectors which would work great for a U2 drive like Intel's Optane 905P, But there's no HW RAID capability for these 2 ports which leaves you to your options as noted. Additionally, there is the M2 port which could either be utilized to augment the OS or in conjunction with the other 2 NMVe storage drives.
One other consideration would be a HCI setup with a pair of these. I run a 2 node HCI with SM's X11SCL-LN4F and E-2176G processor. Storage Spaces Direct is running on 2x Optane 905p, 4x Intel 3700, and 8 Seagate 2.5 1TB drives and I easily see 300K IOPs. The 2 limiting factors with my current setup is Core 0 maxes out trying to manage the I/O and the initial MB support of 64GB max RAM. Even so, I run 2 dozen VMs and the performance is snappier than I could ever hope for. There is a BIOS update to address both issues, just need time to make it happen.
My next HCI iteration will likely be the H11SSL-NC (or predecessor), Epyc Rome 16C CPU and benefit from cores and memory channels/bandwidth. Though I am curious to see how the Rome CPU handles the I/O load...
