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|How NAS works|
The development of NAS
At its most basic level, NAS provides remote file services over a network. The network is usually Ethernet, but can use other technologies as well. From a historical perspective, NAS is file serving as originally developed by Sun with NFS in the mid-1980s. From that point, servers were used as file servers to provide storage for file sharing, typically in engineering or development environments. These special purpose systems took on the moniker network-attached storage.
NAS is storage directly connected to a network such as a LAN that provides file-level access to data using standardized protocols such as NFS or CIFS (see "How NAS works" sidebar). The file system on the NAS server determines the location of the data requested by the application client whether it's in its cache or on the storage. NAS devices often have operating systems optimized for file operations, whether they're customized versions of Unix or Microsoft's Server Appliance Kit (essentially a pared-down version of Windows 2ooo).
While direct-attached storage (DAS) or SANs provide blocks of data for what's termed block I/O, NAS devices handle file I/O where a request is for data from a file with a byte offset into the file. However, storage vendors are starting to build products enabling NAS to handle block transfers of data as well as files.
High-end NAS boxes go beyond the basic capabilities of NAS appliances. For example, many have special handlers to handle multiple operating system and file system protocols, so that the same box can be used to provide storage for both Windows and Unix servers. Redundancy and availability features are also prominent attractions.
Companies are deploying high-end NAS appliances in the following areas:
ISPs - Internet service providers and Web hosting businesses extensively use NAS devices due to the simplicity of administration.
Content delivery - Delivering content, whether it's distribution of software, online news or other material has been a major application of high-end NAS appliances.
Databases - Transaction processing that uses databases has been the target for NAS vendors who want to move up the food chain into the enterprise market. High-end NAS appliances that have the requisite performance and can answer the security concerns of customers have been deployed as solutions for those customers.
Engineering and development - NAS devices are being used for code development, computer aided design and graphic design applications.
Imaging - Imaging is a broad area that includes video editing, prepress and other large file manipulation applications.
NAS gateway - One of the recent trends for NAS devices is using the controller function of NAS - sometimes called a NAS head - as a gateway to the storage on a SAN. The storage part of the NAS - remember, NAS turns a remote file request into a block I/O for its attached disk storage - is part of the storage network in the SAN. Some vendors are calling this SAN and NAS convergence, which is confusing because of other solutions using different technology - but the same terminology. The main advantage of a NAS gateway is the storage administrator can manage the resources differently; in a converged manner, all the storage resources are managed as part of the SAN, which may reduce management costs and overall storage costs.
This was first published in July 2002