Recently I decided to rebuild my own NAS, previously I had an old first generation Celeron system with only 512MB of RAM.
It would use an average of 200Watt or more... not really good for the energy bill.
Sometimes I would also let my computer run for days because of multiple VM's which where running and couldn't / wouldn't be shutdown. Which was also not really helping since this is an AMD Phenom X2...
So the NAS would have to serve my files, manage my network and virtualize some VM's. And hopefully in the end save some money.
I came up with the following hardware specifications:
- Motherboard: ASRock C2750D4I (Atom C2750 2.4 Ghz Octa Core @ 20W with VT-x support)
- RAM: Crucial 16 GB DDR3-1600 Quad-Kit
- PSU: be quiet! Pure Power L8 350W (low noise and good efficiency on 10 a 20 percent load)
- Case: Fractal Design Node 304
- System disk: OCZ Vertex-2 32GB (already in the old system)
- Storage disks: 4x WD Caviar Green 2TB (RAID5 - I know RAID5 has a 55% recovery change with disks above 1.7TB) (already in the old system)
Currently I'm very satisfied by the end result, it's very quite, doesn't use more then 80Watt or so. And it's fast as hell 
Services and Plugins:
- miniDLNA
- FTP
- iSCSI Target
- DNSMasq
- Nginx
- WINS Server
- NFS Server
- SNMP
- SSH
- TFTP
- MySQL
- VirtualBox
ToDo
- OwnCloud
- BackupPC
- CUPS
- Network Monitoring
Pictures
Front View
View Inside
Back View
Placement