Both Storage Area Networks (SANs) and Network Attached Storage (NAS) provide networked storage solutions.
A NAS is a single storage device that operate on data files, while a SAN is a local network of multiple devices that operate on disk blocks.
A SAN commonly utilizes Fibre Channel interconnects. A NAS typically makes Ethernet and TCP/IP connections.
A DAS system is made of a data storage device (for example enclosures holding a number of hard disk drives) connected directly to a computer through a host bus adapter (HBA). Between those two points there is no network device (like hub, switch, or router), and this is the main characteristic of DAS.
The main protocols used for DAS connections are ATA, SATA, eSATA, SCSI, SAS, and Fibre Channel.
Most storage networks use the SCSI protocol for communication between servers and disk drive devices. A mapping layer to other protocols is used to form a network:
ATA over Ethernet (AoE), mapping of ATA over Ethernet
Fibre Channel Protocol (FCP), the most prominent one, is a mapping of SCSI over Fibre Channel
Fibre Channel over Ethernet (FCoE)
ESCON over Fibre Channel (FICON), used by mainframe computers
HyperSCSI, mapping of SCSI over Ethernet
iFCP or SANoIP mapping of FCP over IP
iSCSI, mapping of SCSI over TCP/IP
iSCSI Extensions for RDMA (iSER), mapping of iSCSI over InfiniBand