A Network Attached Storage (NAS) server provides file storage to multiple clients on a network. You can get a Drobo or a Synology device to provide an out-of-the-box experience, but I prefer to have absolute control over both the hardware and software that provide a centralized source of file storage. My choice of software allows me to combine both SAN and NAS functions into one device. If you are asking what is the difference between a SAN and NAS, you can think of it this way. A NAS storage appears to the client as a file server that the client can map drives to. SAN storage appear to the client as a disk that can be managed and treated just like directly-attached storage (DAS)disk. I get iSCSI, NFS, SMB/CIFS features for my workstations, laptops, and virtualization servers. My choice for the operating system is FreeNAS. More information related to the software and management can be found under the Unix section of this web site. As of January 2016, the hardware cost of these systems range from $700 for the entry-level system to $1800 for the high-performance system.
I have three recommendations for motherboard and storage based on the level of performance needed however all use the same case and power supply: