I've managed to resolve the issue. Looking more closely at PERC H330's firmware release notes I noticed the following for version 25.5.6.0009: Fixed an isolated issue where an exception error could occur during boot. The symptoms include a hang during system boot which displays "FW initializing" on screen for two hours or more, and iDRAC LC log reporting "PR8 Device not detected" Perhaps I omitted it on the first reading, because the message was not exactly the same. I checked the firmware versions on my R330 and it turned out they were all the original versions with which the system was shipped. The system was never upgraded according to the Lifecycle log, so I had the following: I first upgraded iDRAC (as this was recommended on Dell's support site). Then, I upgraded BIOS through iDRAC's Update and Rollback. At this point the problem was gone. I rebooted the system successfully two times. Then, I upgraded also PERC H330's firmware. Finally, I rebooted two more times and made a cold start (after returning the USB memory key to the internal USB port). The system is now booting without being stuck at "Initializing Firmware Interfaces..." making me happy again 
A few days ago I bought a second hand Power Edge R330 (having PERCH330 adapter) with the intention to use it as an ESXi host for my work at home. I added up RAM (4x16GB), four Adata SU800 SSD 512GB drives and a SanDisk Cruzer Fit USB Flash Drive 16GB. My setup: RAID5 with the USB Flash on the internal USB port. ESXi 7 free installed on the USB Flash. The problem: After reboot the system is stuck at "Initializing Firmware Interfaces..." for about 5 minutes and then disks failure is reported on Disks 2 to 4. The disks are new. I eject the drives and insert them again, so they become online. Then from BIOS I restore the virtual disk by joining the foreign drives and I'm able to boot normally, but this is not a solution... What I tried so far: I read some articles here and over the Internet suggesting different things. I read the BIOS and PERC H330 firmware change logs, but found nothing related to my problem. The solutions I tried were: In both cases the system reboots normally the first time, but then again the problem described above. Has the community any suggestion what could be the problem? What else could I try? P.S. I first tested the system with ESXi installed on a single old HDD (no RAID) and it worked pretty well. There was no such problem. With the RAID array it works even better handling 16 virtual machines running at once (and more started from time to time) except that I'm not certain that after reboot the system would come up live.
R330 stuck on Initializing Firmware Interfaces for 5mins, then disks failure