A storage-area network (SAN) organizes storage resouces on an independent, high-performance network.
The key distinction between NAS and SANs is that network-attached storage handles input/output (I/O) requests for individual files, whereas a storage-area network manages I/O requests for contiguous blocks of data.
Today, some SANs can transport data over a standard Ethernet connection, but most often storage area networks use the Fibre Channel protocol, which was developed specifically for high-speed data transport on storage-area networks.
NAS, DAS or SAN? Select the Right Storage Technology for Your Organization.
DAS: Ideal for Local Data Sharing Requirements
NAS: File-Level Data Sharing Across the Enterprise
SANs: High Availability for Block-Level Data Transfer
Each has their benefits, but each is best suited for a particular environment.