Here is some feedback on my upgrade from omv 3 to omv 4.
omv3 was running on a Fujitsu D3417-B / Xeon with a HD-Systemdisk and SoftRaid5 3x HD WD Red 8TB.
I installed omv4 on a D3410-B2 / Celeron / SSD-Systemdisk M2 4xPCIe NVMe almost without any quirks. Biggest "issue": no ip-adress after reboot from install -> cmd 'ip a s' showed there was an IP-adress thow it was not announced on the log-in-screen). Everything I could solve by searching the Forum. NVMe was not possible with omv3. Great success of omv4! Then I plugged the three SoftRaid5 HDs and could integrate them without any hussle !!! Great success of omv4!
Thanx for the gread job done with omv 4 !!!