Is It NAS/SAN? Dr SAN/NAS? - network-attached storage, storage area network - Technology Information

Computer Technology Review, June, 2001 by Christine Chudnow

Either way, integrating them makes increasing sense

NAS/SAN integration means more than slapping a Fibre Channel connector on a NAS back-end and calling it a day. NAS and SAN are fundamentally different in technology, constituency, applications, and business requirements.

Networked Attached Storage serves multiple servers by storing file-level data. Using the common protocols NFS and CIFS, it uses TCP/IP and Ethernet to host and control dedicated and direct attached storage with other host systems. NAS benefits include storage and data sharing between multiple hosts and operating systems, application-based storage access at the file level, simpler management by reducing duplicate data and storage, and ignoring distance limitations through networking techniques. Their thin, storage-optimized operating systems are usually proprietary, though Microsoft has recently released an upgrade of its Server Appliance Kit. The software allows OEMs such as Dell and Maxtor to install a stripped-down version of Windows 2000 on their NAS boxes, saving big on development dollars and widening W2000 and NT platform support and integration.

Not all NAS boxes are created equal. In their simplest form they are literally appliances, thin servers with built-in storage. An example of this type is Quantum's low-cost 10GB Snap! Server 1000, weighing in at 3.5 pounds. A mid-tier NAS box would usually contain a Fibre Channel connector on its back-end and increased storage and functionality. Until very recently these boxes were rather expensive at 18 cents/MB, but Dell and Maxtor have recently stormed the mid-tier market with a 2 cents/MB average cost. The high mid-tier and upper-tier is largely held by NetApp's Filers and EMC's Celerras. EMC in particular integrates NAS and SAN as a matter of course--Celerra is a series of thin file servers with a Symmetrix disk subsystem on its back-end.

The NAS user base represents remote offices, departments and workgroups where immediate, shared access to files is the guiding business need. Steve Rogers, vice president of marketing for Connex said, "NAS is about localization of data, not consolidation. People need edge access to data instead of having to go back to the network all the time."

SANs are more loosely defined, but in their simplest form are fast, block-level storage networks. Usually Fibre Channel-based, they sport dedicated servers, storage devices, switches, routers, and other hardware and software components. Key SAN benefits include offloading traffic from the LAN, high speed data transfer, serverless backup, and improved data availability with any-to-any connectivity.

SANs operate in the corporate glass house where administration is far more sophisticated and systems are vastly more expensive.

High-performance database access and transaction processing are most suitable for the SAN These applications manage their own data spaces and require great flexibility on physical data locations and fast direct access to small record sets. They require block-level performance and control to reach optimum performance.

NAS shines when serving applications that require shared access to the same files, such as Internet-based applications and web page serving. In this scenario, many heterogeneous servers are running concurrently, with each accessing the same web pages. Media serving is similar, with the host presenting video streams to many users at the same time.

When Integration Makes Sense

SAN and NAS may be complementary, but with different business objectives, applications and users, not every business requires integration. The decision should revolve around the applications. Greg Schulz of MTI, a vocal vendor of integration products, believes that companies make a mistake when they try to handle their storage and data access solely through a NAS or through a SAN. In his view, the best approach is an integrated system where SAN storage acts as a storage backbone to the front-end NAS, rather than having a SAN attached directly to network host systems. He suggests that different applications require different storage approaches (See table).

The Clipper Group also believes in NAS/SAN integration as an elegant and scalable approach to serving the needs of different users and applications. They suggest three components of a successful integration:

1. Fully tested and supported applications within the integrated storage structure. The infrastructure should be able to handle both centralized and distributed information.

2. Ability to add or re-deploy storage without taking down the system or interrupting data processing.

3. A single administrative interface to manage the mixed-type storage infrastructure.

The figure shows an integrated SAN and NAS environment.

Salomon Smith Barney storage analysts believe that NAS, SAN, and even DAS are giving way to what they term a single Data-Centric architecture. Their original forecast of 2001 was overly optimistic, as true data-centric solutions are extremely difficult to implement given technological, legacy, and financial constraints. Clearly there is an increasing need for NAS/SAN integrated structures with a unified management interface.