Network Attached Storage (NAS)
A NAS unit is essentially a self-contained computer or device connected to a network, with the sole purpose of supplying file-based data storage services to other users on the network. The unit is not designed to carry out general-purpose computing tasks, although it may technically be possible to run other software on it. NAS units usually do not have a keyboard or display, and are controlled and configured over the network, often by connecting a browser to their network address. The alternative to NAS storage on a network is to use a computer as a file server. In its most basic form a dedicated file server is no more than a NAS unit with keyboard and display and an operating system which, while optimized for providing storage services, can run other tasks; however, file servers are increasingly used to supply other functionality, such as supplying database services, email services, and so on. A general-purpose operating system is not needed on a NAS device, and often minimal-functionality or stripped-down operating systems are used.
NAS systems contain one or more hard disks, often arranged into logical, redundant storage containers or RAID arrays (redundant arrays of inexpensive/independent disks). 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) or SMB/CIFS (Server Message Block/Common Internet File System) (used with MS Windows systems). NAS units rarely limit clients to a single protocol.
NAS provides both storage and 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, Fiber Channel, iSCSI, ATA over Ethernet, or HyperSCSI.
Despite differences SAN and NAS are not exclusive and may be combined in one solution: SAN-NAS hybrid
The boundaries between NAS and SAN systems are starting to overlap, with some products making the obvious next evolution and offering both file level protocols (NAS) and block level protocols (SAN) from the same system. However a SAN device is usually served through NAS as one large flat file, not as a true file system.
History
Network Attached Storage was introduced with the early file sharing Novell's NetWare server operating system and NCP protocol in 1983. In the UNIX world, Sun Microsystems' 1984 release of NFS allowed network servers to share their storage space with networked clients. 3Com's 3Server and 3+Share software was the first purpose-built servers (including proprietary hardware, software, and multiple disks) for open systems servers, and the company led the segment from 1985 through the early 1990s. 3Com and Microsoft would develop the LAN Manager software and protocol to further this new market. Inspired by the success of file servers from Novell, IBM, and Sun, several firms developed dedicated file servers. While 3server was among the first firms to build a dedicated NAS for desktop operating systems, Auspex Systems was one of the first to develop a dedicated NFS server for use in the UNIX market. A group of Auspex engineers split away in the early 1990s to create the integrated NetApp filer, which supported both Windows' CIFS and UNIX'es NFS, and had superior scalability and ease of deployment. This started the market for proprietary NAS devices now led by NetApp and EMC Celerra.
Benefits
NAS is useful for more than just
general centralized storage provided to client computers in environments with
large amounts of data. With simpler and lower cost systems coming to market, NAS
is emerging into the home where there is a large amount of multi-media data. Unlike their
rack mounted counterparts, they are generally packaged in smaller form
factors. The price of NAS appliances has plummeted in recent years, offering
flexible network-based storage to the home consumer market for little more than
the cost of a regular
USB or
FireWire external hard disk. Many of these home consumer devices are built
around
ARM, PowerPC
or
MIPS processors running an
embedded Linux
operating system. More recently, home NAS devices have incorporated support
for the
Universal Plug and Play protocol, enabling them to serve the growing number
of networked home media players. As an added bonus, some NAS systems allow you
to access your files not just while you are at home, but anywhere in the world
as long as you have access to the internet. A real benefit to the person who is
on the road and needs the forgotten report.