Jens,
Thanks for that detailed description of your experience with the HP micro server. I also have one N40L model and went a similar route, but rather then using the BIOS hack installed into the one slot a HighPoint Rocket 620 PCI-Express 2.0 x1 SATA III (6.0Gb/s) Controller Card plus in the other slot I stuck a Intel EXPI9301CTBLK 10/ 100/ 1000Mbps PCI-Express Network Adapter just to make sure there are no network bottlenecks plus being able to see if the size of MTU will make a difference. It did not. I have so far installed 4 Hitachi 3TB Cool Spin drives and run 5.b14 and have not experienced any problems yet.
The only observance I have had so far is that writing to the protected array is not as fast as my other UnRaid server that uses Samsung 2TB drives. I chuck this one up to the Hitachi drives just being slower.
Next for me is waiting for the 3TB drives to get cheaper and then also installing the Nexus adapter for 2 additional drives in the optical drive bay.
Thanks again for you write up and this whole thread makes it a lot easier for putting one of these together.
O2G