Platform AMD X399 does not yet support boot from NVMe RAID array
Source found, in his words, «the problem with storing», typical of the AMD platform Ryzen Threadripper HEDT. More precisely, the chipset X399.
As you know, AMD Ryzen Threadripper hefty root complex PCIe 3.0 with 64 lines. Provide throughput sufficient for the most demanding configurations with multiple 3D cards and SSDS, include PCIe. Unfortunately, as it turned out, the initial load of the array NVMe RAID is not supported. Platform capabilities are still limited booting from a separate drive, and if you want to use to load the array, then it needs to be established with the SATA hard drives.
According to one source, the reason that manufacturer did not implement the loading of the array NVMe RAID (verify that the NVMe RAID arrays can be used, but not to download), is that lines of PCIe is physically distributed among the individual crystals Threadripper.
One of the crystals provides some lines for communication with the chipset, to 16 lines each crystal selected for 3D maps, while others are used for high-speed I / o, including USB 3.1, 10 GbE, M. 2 and U. 2. This means that the slots M. 2/U. 2 can be connected to different crystals, resulting in difficulty in ensuring reliable operation of the array at boot. However, according to the second source, AMD promises to add the ability to bootstrap from NVMe RAID array later without naming a specific date.