Hi there, Precision 5820 owner here which has a lot in common with the 7820.  I run 2 x 2TB NVME SSDs in the top two Flexbays in a RAID 0 configuration and boot Windows from them no problem. Also no issues booting from a single NVME either.  Performance is incredible, running your OS and applications on an NVME SSD is the single best thing you can do for a performance increase right now.  I also run a pair of 18TB Seagate Ironwolf HDD’s in the bottom two Flex Bays in a RAID 0 configuration. The system recognises the full 18TB per drive no problem.  My 5820 is an X299 platform with an i9 10980XE CPU, it uses Intel VROC RAID which is/was an enterprise alternative to Intel RST.  You shouldn’t have any issues at all. And yes, the 7820 is PCIE-3.0, PCIE-4.0 was not available on Intel CPUs available with the unit. However the only benefit you’ll really see from that right now is the doubling of bandwidth enabling x4 NVME drives to get upto 8GB/s rather than 4GB/s.
I am a professional photographer using a Precision T7400 workstation as my graphics workstation. I have the OS (Windows 10 Pro), my applications, system files and the like on a Samsung 860 EVO 1TB SSD in a SATA tray in one of the front 5.25: bays, and I keep all of my image and data files on four internal 3.5” WD Black 5TB SATA HDD drives configured via the on-board RAID controller as a pair of 10TB RAID 0 volumes (actually a pair of 4TB volumes, since I discovered after buying the drives that the T7400’s on-board controlled can only recognize up to 2TB drives.) I recently found out that the T7400 will not run the latest version of Photoshop, as Photoshop now requires CPUs with the SSE 4.2 instruction set, and my processors are SSE 4.1.  So, I purchased a used Precision 7820 with dual Silver 4214 processors and Windows 10 Pro but no drives. The easiest transition is to move all 5 of my drives from the T7400 to the 7820, and I don’t foresee any problems configuring the 7820 just like the T7400 is configured now, or am I wrong about that?  I’m hoping the on-board Intel® RSTe controller will recognize the full 5TB size of the WD drives, though I’ve been unable to find a verification of that on the Dell website or in this forum.  If so, I might switch to a single 10TB RAID 10 volume. Before moving the Samsung SSD, though, I wanted to ask for opinions as to whether a newer and faster SSD will provide a noticeable improvement in system performance. If yes, I’m open to specific make/model suggestions, keeping in mind that I value reliability over sheer speed. Alternatively, I’m reading that NVMe drives are much faster than SATA SSDs, so I have 3 questions. Any and all help will be greatly appreciated!
Easy to boot a Precision 7820 from an NVMe drive in the NVMe FlexBay?