I have an Atom D510 running software raid 5 and 2 P2P daemons on a headless Debian stable server. While it functions as a file server, I have not yet turned on NFS. I would have been adequately served by a D410 instead because in my home usage pattern CPU utilization is typically under 15% and typically never reaches 45% other than during upgrades. Interestingly for software Raid 5, my impression is that, for a given file activity, level CPU utilization for parity checking should go down as the number of disks goes up. So my 3 X 2TB configuration is worst case.
Congratulations to those who have finally recognized that Atom is a wimpy chip. I agree and maybe it should never be used unless its performance is exactly what it required and it offers the cheapest (and best supported) and lowest energy use option available like it did for me. My recollection is that I paid under $90 for an itx server class board from Gigabyte with 4 sata ports. Today, Pricewatch has precisely 0 itx motherboards with CPU from someone other than Intel available for under $100.
Also, I do not understand home use of Raid 1 over software Raid 5 for for infrequently accessed media files unless its a Windows thing.