Whitepapers

Network Attached Storage (NAS) and Storage Area Networks (SAN)
What's in a Name?

By Dan Costantini - Hitachi Data Systems Inc. November 11,1999

Information Technology is replete with buzzwords and acronyms, where some may appear to have the same meaning, yet describe completely polarized architectures and methodologies. To enterprise organizations, none is more evident that the 'difference' or 'similarity' of Network Attached Storage (NAS) and Storage Area Networks (SAN).

NAS or SAN? What's in a name?

The movement of information in a client/server enterprise is typically over a network. Corporate information is generally stored on high-speed, high-capacity disk storage arrays which are connected to application servers, that facilitate access to this information is an integrated fashion. With the advent of fibre-channel (FC) technology, enterprises now have a medium that permits them to exploit the use of FC in order to easily control, manage and share corporate information, regardless of heterogeneous platforms, applications and geography, and be able do this in a centralized fashion.
However, as with any new emerging technology, enterprises need to understand the benefits, as well as the business impact of a specific architecture (or in this case: the difference between NAS and SAN) so that their Information Technology goals are aligned with the corporate business direction of their respective organization.

This document has been prepared to provide corporate Information Technology managers and users with a clearer understanding of the different storage connectivity approaches that are offered by both NAS and SAN architectures, and to describe the role of Fibre Channel technology within these architectures.

Network Attached Storage (NAS)

In a NAS architecture, corporate information resides in a storage system that is attached to a dedicated server, which in turn is directly connected to a network, and uses a common communications protocol, such as TCP/IP. In a traditional corporate IT infrastructure, the NAS operates as a server in a typical client/server environment. The NAS is connected to a network by standard connectivity options such as Ethernet, FDDI and ATM. In some cases, a single specialized NAS server can have up to 30 Ethernet connections.

A NAS server (a processor with an operating system) is necessary in order to transfer the data between it and the NAS storage device, and then move the data on to the corporate network. This is done via traditional file I/O protocol. The most common of these protocols are Network File System (NFS) and Common Internet File Service (CIFS).

NFS was originally developed by Sun Microsystems Computer Corp. (SMCC), and is now part of the Open Network Computing (ONC) initiative. It is the most common file access protocol to access shared files in a UNIX environment. CIFS is a file access protocol designed for the Internet, and based on the Server Message Block (SMB) protocol used by the Microsoft Windows operating system. CIFS does not replace the use of NFS, but rather complements it, because of its ability to provide synchronization between client and server.

Although a NAS with NFS can be implemented on readily available tightly-coupled server and disk storage arrays, there are actually only three (3) major vendors that currently have a large marketshare of the NAS marketspace. They are: Network Appliance (also known as NetApps), Auspex Systems, and Sun Microsystems. Both NetApps and Auspex use proprietary tightly integrated servers and storage devices. In the majority of cases, the Sun implementation uses a dedicated Sun server, and typically connected to external Sun storage; although any external storage that is certified to be connected to a Sun server can also be used. However, this is not the case with NetApps or Auspex, as additional storage requirements must be acquired from the respective NAS vendor.

The NAS server permits multiple clients to share files, since clients can access files as if they were local files, with the exception that they must be accessed over a network. In this way, common files can be maintained in a central location, and accessed by many clients, which eliminates the need for multiple copies of files on multiple client systems. In addition, this improves data integrity, data security and reduces costly duplication of files. Major applications that benefit from the use of NAS to share large amounts of information include CAD/CAM (Computer Aided Design/Computer Aided Manufacturing), document management, imaging as well as other similar application serving environments.

Because data travels over the network, NAS is not always suitable for applications such as data warehouses and On-Line Transaction Processing (OLTP), since these applications need to sustain high I/O data rates with little, or no degradation in response times to the clients.

Storage Area Networks (SAN)

Unlike a NAS, a SAN does not function like a server. A SAN facilitates the movement of data, between a storage subsystem and a server, via a shared access network. Also, unlike a NAS, a SAN utilizes industry file protocols (such as SCSI or ESCON) that were designed specifically for the high-speed movement of information between single/multiple servers and single/multiple disk storage arrays.

The SAN is the new evolution of harnessing the power, flexibility and scalability of server/storage interaction, and it is tied directly to the use of the Fibre-Channel topology. Fibre Channel is the key enabling technology that brings networking concepts to the standard server/storage connectivity model. It provides higher bandwidth, greater distance separation and increased connectivity. In most cases, a SAN also permits the addition/deletion of server and storage devices with no disruption to the current applications in production. This is due to the advent of fabric switch technologies that permit enterprises to embark upon a seamless and integrated server/storage architecture for their organizations. Fibre Channel switches, are devices that consist of multiple ports, and provide automated connectivity between nodes on a Fibre Channel network. In 1999, several vendors have brought to market robust Fibre Channel switch architectures that deliver the promise of a seamless and integrated server/storage architecture.

Some of the major Fibre Channel switch vendors include: Brocade Communications, Ancor Communications, Gadzoox Networks, Vixel Corporation, and McData Corporation.

NAS in a SAN?

As stated previously, a NAS performs a specialized function for specific applications to meet the needs of a corporate enterprise. A SAN is primarily geared towards helping these corporate enterprises gain sophisticated control over their information in order to provide them with the flexibility to optimally share, manage and protect all of their corporate data in a centralized manner. Organizations need to have the flexibility to select and implement solutions that will allow them to achieve their corporate business goals. In all cases, a SAN is optimally positioned to respond to this challenge.

Some of the initiatives that have been requested by enterprises go beyond the requirements of a NAS. These include: the seamless replication of information to provide non-disruptive access to 'point-in-time' copies of data providing a business continuity model with the ability to replicate information over a geography, while at the same time being able to maintain data integrity and currency performing disaster recovery and backup functions without impacting the corporate network being able to share information across heterogeneous platforms without impacting the corporate network non-disruptive change management by being able to easily add/delete server/storage requirements regardless of application platform. A NAS can avail itself of the power of a SAN architecture by locating corporate information in a single, or multiple centralized Enterprise Storage subsystem(s), and can therefore respond to the indicated corporate enterprise requirements. A visual representation of such an environment is as follows:

Summary

Over the next few years, with more and more organizations facing an explosion in storage growth, and the management issues that accompany this growth, the Fibre Channel topology and the SAN architecture are being viewed as the solutions to be able to effectively meet these challenges. The ability to reliably move data over greater distances, and at higher speeds, without impacting the corporate network of an enterprise, now permits organizations to consolidate, connect and manage a large amount of systems to a centralized Enterprise Storage repository.

The moment that Enterprise Storage can be consolidated in such a fashion, it permits organizations to embark upon initiatives such as business continuity, backup-and-restore and server consolidation without impacting network resources and improving the ability for enterprises to flexibly respond to the business challenges of the future.

Copyright Hitachi Data Systems Inc. - November 11,1999