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Smart Advice: Storage Attachment Made To Order

Expect iSCSI to gain popularity at Fibre Channel SANs' expense, The Advisory Council says. Also, plan your migration to Microsoft Exchange 2003 carefully, and recognize possible need for coexistence of messaging systems during the migration.

Editor's Note: Welcome to SmartAdvice, a weekly column by The Advisory Council (TAC), an advisory service firm. The feature answers two questions of core interest to you, ranging from career advice to enterprise strategies to how to deal with vendors. Submit questions directly to

Question A: When is it appropriate to use each of the various storage-attachment technologies?

Our advice: Beth CohenThere just never seems to be enough data storage available, so you have to consider when it's appropriate to use each of the various storage-attachment technologies. Vendors have responded to this need with a confusing variety of products--direct-attached storage, network-attached storage, storage area networks, and Internet Small Computer System Interface, or iSCSI. Your company's particular mix of storage-attachment technologies should be based on specific requirements for economy, speed, ease of use, and storage-management tools.

Direct-attached storage is the original method of attaching storage devices to midrange computers and PCs. Rather than through a network, it's physically connected to a computer by a variety of standard interfaces, including Advanced Technology Attachment and Integrated Drive Electronics, two PC disk-drive technologies, along with Serial ATA and SCSI connections. For companies with only a few servers and limited storage needs, direct-attached storage is a proven technology that's simple, secure, and economical, with system capacities that range up to 4 terabytes. The disadvantages are poor data protection and limited growth options.

Related Links

iSCSI and SATA a Dynamic Duo

NAS, DAS Or SAN? - Choosing The Right Storage Technology For Your Organization

Virtual Storage, Real Uneasiness

Secure Storage Must Be A Higher Priority

Network-attached storage appliances are accessed directly from an IP network. They work well in workgroup and small-business environments because of their easy installation and administration, and they scale modularly. Data-intensive applications can degrade network performance, and they work poorly on lower-bandwidth networks (less than 10 Mbps). System capacities range up to 4 terabytes. Network-attached storage devices tend to have limited management capabilities.

Storage area networks are attached to servers through high-speed Fibre Channel networks, delivering the performance needed for data-intensive applications. Their modular designs and high capacities (hundreds of terabytes) allow for security, scalability, and redundancy, but they have limited wide area networking capabilities, and Fibre Channel hardware is relatively expensive.

The latest entry in storage attachment is Internet Small Computer System Interface. Like network-attached storage, iSCSI uses IP networks, but optimizes device access by sending highly efficient, standard SCSI commands over the network. Depending on your performance needs, iSCSI devices can be configured either on a dedicated IP network or through the company network. Since IP networks are ubiquitous, iSCSI offers the promise of truly location-independent data storage and retrieval. The technology is gaining popularity because of its low cost, high speed, and sophisticated management tools.

The type of data storage that you choose is going to depend on your specific requirements. Network-attached storage and direct-attached storage will maintain their low-cost niches for workgroups and smaller companies. Expect to see iSCSI gain popularity at the expense of Fibre Channel SANs, because it offers the best of both network-attached storage and storage area networks--scalability, flexible architecture, access speed, and management tools--at a much lower cost.

--Beth Cohen

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