Network-attached storage (NAS) is a file-level computer data storage server connected to a computer network providing data access to a heterogeneous group of clients. NAS  is specialized for serving files either by its hardware, software, or configuration. It is often manufactured as a computer appliance – a purpose-built specialized computer.[nb 1] NAS systems are networked appliances which contain one or more storage drives, often arranged into logical, redundant storage containers or RAID.
Network-attached storage removes the responsibility of file serving from other servers on the network. They typically provide access to files using network file sharing protocols such as NFS, SMB/CIFS, or AFP. From the mid-1990s, NAS devices began gaining popularity as a convenient method of sharing files among multiple computers. Potential benefits of dedicated network-attached storage, compared to general-purpose servers also serving files, include faster data access, easier administration, and simple configuration.
Network Attached Storage ( NAS) and Storage Area Network ( SAN) Solutions
A storage area network (SAN) is a dedicated network that provides access to consolidated, block level data storage. SANs are primarily used to enhance storage devices, such as disk arrays, tape libraries, and optical jukeboxes, accessible to servers so that the devices appear like locally attached devices to the operating system. A SAN typically has its own network of storage devices that are generally not accessible through the local area network (LAN) by other devices. The cost and complexity of SANs dropped in the early 2000s to levels allowing wider adoption across both enterprise and small to medium sized business environments.
SAN compared to NAS
Network-attached storage (NAS) was designed before the emergence of SAN as a solution to the limitations of the traditionally used direct-attached storage (DAS), in which individual storage devices such as disk drives are connected directly to each individual computer and not shared. In both a NAS and SAN solution the various computers in a network, such as individual users' desktop computers and dedicated servers running applications ("application servers"), can share a more centralized collection of storage devices via a network connection through the LAN.
Concentrating the storage on one or more NAS servers or in a SAN instead of placing storage devices on each application server allows application server configurations to be optimized for running their applications instead of also storing all the related data and moves the storage management task to the NAS or SAN system. Both NAS and SAN have the potential to reduce the amount of excess storage that must be purchased and provisioned as spare space. In a DAS-only architecture, each computer must be provisioned with enough excess storage to ensure that the computer does not run out of space at an untimely moment. In a DAS architecture the spare storage on one computer cannot be utilized by another. With a NAS or SAN architecture, where storage is shared across the needs of multiple computers, one normally provisions a pool of shared spare storage that will serve the peak needs of the connected computers, which typically is less than the total amount of spare storage that would be needed if individual storage devices were dedicated to each computer.
In a NAS solution the storage devices are directly connected to a "NAS-Server" that makes the storage available at a file-level to the other computers across the LAN. In a SAN solution the storage is made available via a server or other dedicated piece of hardware at a lower "block-level", leaving file system concerns to the "client" side. SAN protocols include Fibre Channel, iSCSI, ATA over Ethernet (AoE) and HyperSCSI. One way to loosely conceptualize the difference between a NAS and a SAN is that NAS appears to the client OS (operating system) as a file server (the client can map network drives to shares on that server) whereas a disk available through a SAN still appears to the client OS as a disk, visible in disk and volume management utilities (along with client's local disks), and available to be formatted with a file system and mounted.
One drawback to both the NAS and SAN architecture is that the connection between the various CPUs and the storage units are no longer dedicated high-speed busses tailored to the needs of storage access. Instead the CPUs use the LAN to communicate, potentially creating bandwidth bottlenecks.
While it is possible to use the NAS or SAN approach to eliminate all storage at user or application computers, typically those computers still have some local Direct Attached Storage for the operating system, various program files and related temporary files used for a variety of purposes, including caching content locally.
To understand their differences, a comparison of DAS, NAS and SAN architectures may be helpful.
NAS and san Both Provide storage for File system. To understand the difference we request you to watch the San san Video. Small business can benefit siginifactly from Nas and San storage. Please contact us for consultation and initial meeting, one of our engineers will be happy to contact you.
Ref: HOW NAS and SAN are Different- A Tutorial Introduction - https://www.youtube.com/watch?v=csdJFazj3h0