Thin NAS Box ( Backup System With Raid or Mirror Option )
Network-attached storage (NAS) is file-level computer data storage connected to acomputer network providing data access to heterogeneous clients. As of 2010 NAS devices are gaining popularity, as a convenient method of sharing files between multiple computers.[1] Potential benefits of network-attached storage, compared to file servers, include faster data access, easier administration, and simple configuration.[2]

NAS systems are networked appliances which contain one or more hard drives, often arranged into logical, redundant storage containers or RAID arrays. 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.

Description
A NAS unit is a computer connected to a network that only provides file-based data storage services to other devices on the network. Although it may technically be possible to run other software on a NAS unit, it is not designed to be a general purpose server. For example, NAS units usually do not have a keyboard or display, and are controlled and configured over the network, often using a browser.[3]

A fully-featured operating system is not needed on a NAS device, so often a stripped-down operating system is used. For example,FreeNAS, an open source NAS solution designed for commodity PC hardware, is implemented as a stripped-down version of FreeBSD.

NAS systems contain one or more hard disks, often arranged into logical, redundant storage containers or RAID arrays. NAS removes the responsibility of file serving from other servers on the network.

NAS uses file-based protocols such as NFS (popular on UNIX systems), SMB/CIFS (Server Message Block/Common Internet File System) (used with MS Windows systems), or AFP (used with Apple Macintosh computers). NAS units rarely limit clients to a single protocol.

NAS vs DAS
The key difference between direct attached storage (DAS) and NAS is that DAS is simply an extension to an existing server and is not necessarily networked. NAS is designed as an easy and self-contained solution for sharing files over the network.

Both DAS and NAS can potentially increase availability of data by using RAID or clustering.

When both are served over the network, NAS could have better performance than DAS, because the NAS device can be tuned precisely for file serving which is less likely to happen on a server responsible for other processing. Both NAS and DAS can have various amount of cache memory, which greatly affects performance. When comparing use of NAS with use of local (non-networked) DAS, the performance of NAS depends mainly on the speed of and congestion on the network.

NAS is generally not as much customizable in terms of hardware (CPU, memory, storage components) or software (extensions, plug-ins, additional protocols) as a general purpose server supplied with DAS.

[edit]NAS vs SANVisual differentiation of NAS vs. SAN use in network architecture.
NAS provides both storage and a file system. This is often contrasted with SAN (Storage Area Network), which provides only block-based storage and leaves file system concerns on the "client" side. SAN protocols are SCSI, Fibre Channel, iSCSI, ATA over Ethernet (AoE), orHyperSCSI.