My first go with NAS4Free was with an off-lease refurbished HP DL180 G6 server that I've tried some "upgrades" to, but I ran into a few snags along the way that I'm wondering how to get past (if it is even possible).
I first replaced the motherboard with one from an HP P4300/SE1220 (because the baseboard management controller on the 100 series HP servers really sucks, the motherboard was a drop-in replacement for the physical form factor, the LO100 BMC on the old board required a $200 license to unlock its features, and it still would have virtual media or full remote KVM, but the alternate board was only $120, and the advance license pack for iLO was only $40 on ebay!).
Powered it up, booted off of the HP systems update media to update all the firmware and bios, and it identified everything just fine and updated everything except the BMC, but throwing a temporary install of Windows 2008 on solved that too -- HP's Linux support isn't as comprehensive as their Windows Server support is...
At this point, spirits and confidence are both high that this is really going to work, and work on the first try
BUT then I chose to replace the P410 RAID controller with an LSI 9280 4i4e that I had available, and all my drives disappeared! Further troubleshooting turned up that the HP expander built into the backplane wouldn't talk to the LSI controller card, and so far, there hasn't been anything I could do about it! 
Has anyone else tried using and HP DL180 G6 chassis for NAS4Free, and if so, what controllers or HBAs have you found to work (if you changed them from the stock P410, etc.? The FreeBSD docs for the ciss(4) driver suggest that it is limited by the controller not supporting or adhering to standards, but it is still listed as working. Unfortunately, I've also had a drive failure in this system since I built it, and I've never seen any indication from NAS4Free that it was aware or had been informed by the HP controller that anything was amiss?
I'd really love to switch over to my LSI controller if possible, does anyone know if this is somehow possible? At least that controller can be relied upon to email me on a failure...