I run FreeNAS (FreeBSD based) on HP Microservers. ECC RAM, 4 drive bays, ...
The older Gen8 boxes Just Work.
With FreeBSD, the newer Gen10 boxes would hang the first time you boot, you need to pause it and set the hw.pci.realloc_bars loader variable to 1. Haven't tried a new install recently.
Details here: https://www.virten.net/2017/10/fix-for-freenas-on-hpe-micros...
Want to buy some pens?