Storage

Several new methods of utilizing computer networks for data storage have emerged in recent years. One popular approach, Network Attached Storage (NAS), allows homes and businesses to store and retrieve large amounts of data more affordably than ever before. NAS challenges the traditional 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."

Central file servers use basic client/server networking technologies to solve these data storage problems. In its simplest form, a file server consists of PC or workstation hardware running a network operating system (NOS) that supports controlled file sharing (such as Novell NetWare, UNIX® or Microsoft Windows). Hard drives installed in the server provide gigabytes of space per disk, and tape drives attached to these servers can extend this capacity even further.

File servers boast a long track record of success, but many homes, workgroups and small businesses cannot justify dedicating a fully general-purpose computer to relatively simple data storage tasks. Enter NAS.

Like traditional 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 NOS. 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 a NAS over an Ethernet connection. The NAS appears on the network as a single "node" that is the IP address of the head device.

A NAS can store any data that appears in the form of files, such as email boxes, Web content, remote system backups, and so on. Overall, the uses of a NAS parallel those of traditional file servers.

NAS systems strive for reliable operation and easy administration. They often include built-in features such as disk space quotas, secure authentication, or the automatic sending of email alerts should an error be detected. NAS Protocols

Communication with a NAS head occurs over TCP/IP. More specifically, clients utilize 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 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.

NAS vs. Traditional File Servers Proponents of NAS claim that NAS technology provides these advantages over traditional file servers:

* lower cost

* better security

* higher availability (less downtime)

* easier to use and administer

NAS products improve on traditional file servers generally through the principle of simplification. By stripping out all of the unnecessary capabilities of a general purpose server -- applications, services or daemons, and hardware peripherals -- a NAS device becomes less prone to system "crashes" and security attacks. When a problem does occur, a NAS system can be diagnosed and rebooted much faster due to its lower level of complexity.

NAS products also generally hide the operating system personality of the device. Whereas Windows, UNIX and NetWare file servers each demand specific protocol support on the client side, NAS systems strive for greater operating system independence of clients.

Opponents of NAS emphasize that traditional file servers have a proven record of success compared to this new breed of "upstart" NAS systems. High-end file systems also contain more processing power than a NAS device, giving servers a performance edge (in terms of transactions or I/O per second rates) over NAS. NAS vs. SAN

At a high level, Storage Area Networks (SANs) serve the same purpose as a NAS system. A SAN supplies data storage capability to other network devices. Traditional SANs differed from traditional NAS in several ways. Specifically, SANs often utilized Fibre Channel rather than Ethernet, and a SAN often incorporated multiple network devices or "endpoints" on a self-contained or "private" LAN, whereas NAS relied on individual devices connected directly to the existing public LAN. The traditional NAS system is a simpler network storage solution, effectively a subset of a full SAN implementation.

The distinction between NAS and SAN has grown fuzzy in recent times, as technology companies continue to invent and market new network storage products. Today's SANs sometimes use Ethernet, NAS systems sometimes use Fibre Channel, and NAS systems sometimes incorporate private networks with multiple endpoints. The primary differentiator between NAS and SAN products now boils down to the choice of network protocol. SAN systems transfer data over the network in the form of disk blocks (fixed-sized file chunks, using low-level storage protocols like SCSI) whereas NAS systems operate at a higher level with the file itself. Conclusion

The new breed of NAS networking products has succeeded in providing a reasonable alternative to traditional file servers in client/server networks. Entry-level NAS products containing 20-50 gigabytes of storage can be purchased for $500 (USD) or less, whereas mid-range and high-end NAS systems can run in the tens of thousands of dollars. Besides cost, a NAS promises reliable operation and easy management. Look for the Network Attached Storage technology to keep evolving as the field matures over the next several years.