NAS(Network-attached storage)
A NAS unit is a computer connected to a network that only provides file-based data storage services to other devices on the network.
As of 2010 NAS devices are gaining popularity, as a convenient method of sharing files among multiple computers.Potential benefits of network-attached storage, compared to file servers, include faster data access, easier administration, and simple configuration.
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. 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.
由于NAS是仅仅用于存储的计算机，因此NAS的操作系统也相对功能单一，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一般也不会有显示器和键盘，而是通过Brower远程配置或控制。NAS的软硬件通常也都是不可定制的。
NAS和DAS的区别
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.
NAS和SAN的区别
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.
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.
即NAS已经提供了文件系统，对于不同的客户端操作系统来说，都是透明的（unix，windows都可直接使用）。但是SAN只提供存储，需要客户端操作系统format和mount。