Precisely speaking, it should be called NAS unit(server) because a NAS device need both Hardware(CPU, memory, storage components) and Software(stripped-down OS).
A NAS unit is a computer connected to a network that provides only file-based data storage services to other devices on the network.
NAS units usually do not have a keyboard or display, and are controlled and configured over the network, often using a browser
- Allows application server to be optimized by move the storage management task out from application server
- The storage devices are directly connected to a "NAS-Server" that makes the storage available at a file-level
- It is often manufactured as a computer appliance – a purpose-built specialized computer
- Typically provide access to files using network file sharing protocols such as NFS, SMB/CIFS, or AFP
- Cost is much lower than SAN
- Flexible and extendable than SAN
Storage area Network
SAN is a network which provides access to consolidated, block level data storage. It's more infrastructure related.
A SAN typically has its own network of storage devices that are generally not accessible through the local area network (LAN) by other devices.
- Allows application server configurations to be optimized by move the storage management task out from application server
- The storage is made available via a server or other dedicated piece of hardware at a lower block-level
- SANs often use a Fibre Channel fabric topology. A typical Fibre Channel SAN fabric is made up of a number of Fibre Channel switches
- SAN protocols include Fibre Channel, iSCSI, ATA over Ethernet (AoE) and HyperSCSI.
- Faster than NAS