Network storage

Network-attached storage

Not to be confused with Storage area network.
A Netgear NAS
Network-attached storage (NAS) is a file-levelcomputer data storage server connected to acomputer network providing data access to aheterogeneous 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, orAFP. 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.[1]
The hard disk drives with "NAS" in their name are functionally similar to other drives but may have different firmware, vibration tolerance, or power dissipation to make them more suitable for use in RAID arrays, which are often used in NAS implementations.[2] For example, some NAS versions of drives support a command extension to allow extended error recovery to be disabled. In a non-RAID application, it may be important for a disk drive to go to great lengths to successfully read a problematic storage block, even if it takes several seconds. In an appropriately configured RAID array, a single bad block on a single drive can be recovered completely via the redundancy encoded across the RAID set. If a drive spends several seconds executing extensive retries it might cause the RAID controller to flag the drive as "down" whereas if it simply replied promptly that the block of data had a checksum error, the RAID controller would use the redundant data on the other drives to correct the error and continue without any problem. Such a "NAS" SATA hard disk drive can be used as an internal PC hard drive, without any problems or adjustments needed, as it simply supports additional options and may possibly be built to a higher quality standard (particularly if accompanied by a higher quoted MTBF figure and higher price) than a regular consumer drive.

DescriptionEdit

Most modern routers have USB ports that can attach USB-powered hard drives for network-wide storage and media streaming.
A NAS unit is a computer connected to a network that provides only 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 usually 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 full-featured operating system is not needed on a NAS device, so often a stripped-down operating system is used. For example,FreeNAS or NAS4Free, both open source NAS solutions designed for commodity PC hardware, are implemented as a stripped-down version of FreeBSD.
NAS systems contain one or more hard disk drives, often arranged into logical, redundant storage containers or RAID.
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),AFP (used with Apple Macintosh computers), or NCP (used with OES and Novell NetWare). NAS units rarely limit clients to a single protocol.

Versus DASEdit

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 orclustering.
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 customizable in terms of hardware (CPU, memory, storage components) or software (extensions, plug-ins, additional protocols) as a general-purpose server supplied with DAS.

Versus SANEdit

Visual differentiation of NAS vs. SANuse 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 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.
Despite their differences, SAN and NAS are not mutually exclusive and may be combined as a SAN-NAS hybrid, offering both file-level protocols (NAS) and block-level protocols (SAN) from the same system. An example of this is Openfiler, a free software product running on Linux-based systems. A shared disk file system can also be run on top of a SAN to provide filesystem services.

HistoryEdit

In the early 1980s, the "Newcastle Connection" by Brian Randell and his colleagues at Newcastle Universitydemonstrated and developed remote file access across a set of UNIX machines.[4][5]Novell's NetWare server operating system andNCP protocol was released in 1983. Following the Newcastle Connection, Sun Microsystems' 1984 release of NFS allowed network servers to share their storage space with networked clients. 3Com and Microsoftwould develop the LAN Manager software and protocol to further this new market. 3Com's3Server and 3+Share software was the first purpose-built server (including proprietary hardware, software, and multiple disks) for open systems servers.
Inspired by the success of file servers from Novell, IBM, and Sun, several firms developed dedicated file servers. While 3Com 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 the Windows CIFS and the UNIX NFS protocols, and had superior scalability and ease of deployment. This started the market for proprietary NAS devices now led by NetApp and EMC Celerra.
Starting in the early 2000s, a series of startups emerged offering alternative solutions to single filer solutions in the form of clustered NAS – Spinnaker Networks (acquired by NetApp in February 2004),Exanet (acquired by Dell in February 2010),Gluster (acquired by RedHat in 2011), ONStor(acquired by LSI in 2009), IBRIX (acquired byHP), Isilon (acquired by EMC – November 2010), PolyServe (acquired by HP in 2007), and Panasas, to name a few.
In 2009, NAS vendors (notably CTERA Networks[6][7] and Netgear) began to introduce online backup solutions integrated in their NAS appliances, for online disaster recovery.[8][9]

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