How Storage Evolved
In the early years of the computer revolution, floppy drives were widely used to share data files. Today, however, the average person’s storage needs far exceed floppy capacities. Businesses now maintain an increasingly large number of electronic documents and presentation sets, including video clips. Home computer users, with the advent of MP3 music files and JPEG images, also require vastly greater and more convenient storage. Central file servers use basic client/server networking technologies to solve some of these data storage problems. In its simplest form, a file server consists of PC or workstation hardware running a network operating system that supports controlled file sharing. Hard drives installed in the server provide gigabytes of space per disk, and tape drives attached to these servers can further extend this capacity. File servers boast a long track record of success, but many homes, workgroups, and small businesses can’t justify dedicating a fully general-purpose computer to relatively simple data storage tasks. Here’s where NAS comes into play.
What Is NAS?
NAS challenges the conventional file-server approach by creating systems designed specifically for data storage. Instead of starting with a general-purpose computer and configuring or removing features from that base, NAS designs begin with the bare-bones components necessary to support file transfers and add features from the bottom up. Like other file servers, NAS follows a client/server design. A single hardware device, often called the NAS box or NAS head, acts as the interface between the NAS and network clients. These NAS devices require no monitor, keyboard, or mouse. They generally run an embedded operating system rather than a full-featured network operating system. One or more disk (and possibly tape) drives can be attached to many NAS systems to increase total capacity. Clients always connect to the NAS head, however, rather than to the individual storage devices. Clients generally access the NAS over an Ethernet connection. The NAS appears on the network as a single “node,” which is the head device’s IP address. The NAS can store any data that appears in the form of files, such as email inboxes, web content, remote system backups, and more. Overall, NAS uses parallel those of traditional file servers.
NAS Protocols
Communication with the NAS head occurs over TCP/IP. More specifically, clients use any of several higher-level protocols (application or layer seven protocols in the OSI model) built on top of TCP/IP. The two application protocols most commonly associated with NAS are the Sun Network File System (NFS) and Common Internet File System (CIFS). Both NFS and CIFS operate in client/server fashion. Both predate the modern NAS by many years; original work on these protocols took place in the 1980s. NFS was developed originally for sharing files between UNIX systems across a LAN. Support for NFS soon expanded to include non-UNIX systems; however, most NFS clients today are computers running some flavor of the UNIX operating system. The CIFS was formerly known as Server Message Block (SMB). SMB was developed by IBM and Microsoft to support file sharing in DOS. As the protocol became widely used in Windows, the name changed to CIFS. This same protocol appears today in UNIX systems as part of the Samba package. Many NAS systems also support Hypertext Transfer Protocol (HTTP). Clients can often download files in their web browser from a NAS that supports HTTP. NAS systems also commonly employ HTTP as an access protocol for web-based administrative user interfaces.
