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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 [email protected]

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.

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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

Question B: What issues must we address in planning a migration to Microsoft Exchange 2003?

Our advice: You're not alone in still being in the planning stage of your migration to Exchange 2003. It's been estimated that, as of year-end 2004, 40% of Exchange mailboxes are still on Exchange 5.5, 43% are on Exchange 2000, and only 14% are on Exchange 2003.

Messaging is a critical application in almost all organizations. It's imperative that your migration be seamless and transparent to both your internal users and external correspondents. If there's an interruption, you'll hear about it right away. Migrations can cause serious outages if you don't plan carefully.

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If your migration is large enough that you can't move all the users in a single operation, then you must deal with the complexity of co-existence. During co-existence, both messaging systems must appear as a single system to all users, address lists must be synchronized, and mail must flow seamlessly. There are three main paths in which messages flow: inbound from the Internet, outbound to the Internet, and between the existing mail system and the new Exchange servers.

Messages between Exchange and a "foreign" system are typically handled by Exchange Connectors. Exchange provides a suite of connectors to handle just about any non-Microsoft messaging system. A connector tricks the foreign messaging system into thinking the Exchange Organization is of the same-breed mail system. Exchange will use the foreign-messaging system's addressing scheme. Exchange's Connectors are well documented in the Microsoft Exchange library.

Sending mail to the Internet from both Exchange and the foreign-messaging system is usually simple. Just make sure your firewall is configured to permit outbound Simple Mail Transfer Protocol from your new servers.

Inbound Internet mail routing is the most difficult aspect of co-existence, because you will be sharing SMTP name spaces with recipients spanning both messaging systems. Most systems want to be authoritative for any SMTP name space for which they're configured to accept mail. How will the messages get from the Internet to recipients in the other system? The way you will build this depends on the migration tool you use.

Here are some other points to prepare your organization for migration:

  • Test, test, and then test some more. The time you spend in the lab will pay back 100 times over in the time you spend on the production system.
  • For each target storage group, plan to back up many times during the migration to clear the transaction logs. Many people think that frequent backups are too much overhead, so a more realistic approach would be to turn on circular logging. Do not forget to turn circular logging off at the end!
  • Expect to open a support case or two with Microsoft. Despite any engineer's level of expertise, this is almost inevitable. Most migrations are such complex operations that there are just some things you can't fix.
  • Evaluate your migration tool thoroughly. I've seen many companies backed into a corner because they didn't understand how their migration tool handled specific Exchange functions such as public-folder E-mail addresses, foreign-language mailboxes, or inbox rules. You'll either catch these in the lab, or be overwhelmed by a backlash from users when they find out something doesn't work like the old system.
  • -- Brian O'Neil

    Beth Cohen, TAC Thought Leader, has more than 20 years of experience building strong IT-delivery organizations from user and vendor perspectives. Having worked as a technologist for BBN, the company that literally invented the Internet, she not only knows where technology is today but where it's heading in the future.

    Brian O'Neil, TAC Expert, has more than 10 years experience in IT designing, migrating, and managing enterprise network infrastructures for the U.S. Department of Defense, financial organizations, medical institutions, and law firms. He has been the primary technical lead and project manager for large migrations to Microsoft Active Directory and Exchange 2003.

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