Network-attached storage

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Network-attached storage (NAS)

A term used to refer to storage elements that connect to a network and provide file access services to computer systems. A NAS Storage Element consists of an engine, which implements the file services, and one or more devices, on which data is stored. NAS elements may be attached to any type of computer network. When attached to SANs, NAS elements may be considered to be members of the Server Attached Storage (SAS) class of storage elements.
A class of systems that provide file services to host computers. A host system that uses network attached storage uses a file system device driver to access data using file access protocols such as NFS or CIFS. NAS systems interpret these commands and perform the internal file and device I/O operations necessary to execute them.

NAS systems are generally computing-storage devices that can be accessed over a computer network (usually TCP/IP), rather than directly being connected to the computer (via a computer bus such as SCSI). This enables multiple computers to share the same storage space at once, which minimizes overhead by centrally managing hard disks. NAS systems usually contain one or more hard disks, often arranged into logical, redundant storage containers or RAID arrays.

The protocol used with NAS is a file based protocol such as NFS or Microsoft's Common Internet File System (CIFS). In reality, there is a miniature operating system on the device such as DART on EMC's Celerra devices or Data ONTAP on NetApp NAS devices.

A storage area network (SAN) is very similar, except it uses a block-based protocol and generally runs over an independent, specialized storage network.

NAS devices become logical file system storage for a local area network. Thus the performance of NAS devices depends heavily on cached memory (the equivalent of RAM) and network interface overhead (the speed of the router and network cards). The benefit is that the device can become a giant neighborhood hard drive for a whole building. The disadvantage is that any constrictions in the local network will slow down the resulting access time.

NAS was developed to address problems with direct attached storage, which included the effort required to administer and maintain "server farms", and the lack of scalability, reliability, availability, and performance. They can deliver significant ease of use, provide heterogeneous data sharing and enable organizations to automate and simplify their data management.

In addition, the price of NAS appliances has plummeted in recent years, offering flexible network based storage to the home consumer for little more than the cost of a regular USB or Firewire external hard disk.

1 NAS applications
2 NAS Vendors
3 NAS for SOHO (Small Office/Home Office)
4 See also
5 External Links

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NAS applications

NAS allows multiple server access through a file-based protocol. This allows administrators to implement simple and low cost load-balancing and fault-tolerant systems.

For example:

Corporate e-mail system with multiple, load-balanced webmail servers
Load-balanced web servers access the same contents from NAS storage

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NAS Vendors

NAS was pioneered by Auspex, based on the success of file servers from Novell, IBM, and Microsoft. The widespread success of NAS was due to the introduction of the Network Appliance Filer, and NAS market share in enterprise storage is increasing due to low total cost of ownership compared to Fibre Channel SANs. In recent years, emerging companies like Coraid, ONStor, ALLNET USA and BlueArc have combined the ease of management of NAS with the performance and scalability of SANs.

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NAS for SOHO (Small Office/Home Office)

NAS are becoming popular for Home and Small Business use. Today, you can buy simple NAS-solutions like the popular Linksys NSLU-2. For people who have old computers they do not use anymore, there are some free NAS servers to download from the internet, like FreeNas or NASLite. They are easy to configure via Webinterface and run on even the slowest computers.

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