Lesson 2: Migration Terminology

This lesson introduces several ways that you can perform a migration. This subject is covered in greater depth in Chapters 6–9 on upgrading and restructuring domains.

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After this lesson, you will be able to

• Understand terms such as upgrade and restructure in the context of migration.

Estimated lesson time: 30 minutes

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Prior to the migration process, you will have a Windows NT–based infrastructure that's organized into some domain structure. This structure serves as the security and management environment for users and resources. These domains usually perform the following tasks:

• Interoperate via a mechanism called a trust
• Consist of versions of Windows NT acting as primary domain controllers (PDCs), backup domain controllers (BDCs), and resource servers linked by network connections

During the migration, you might be running both Windows 2000 and Windows NT servers in what is known as mixed mode. When you remove the last Windows NT domain controller from the network, you can convert the entire network to native mode. Moving to native mode is a one-way transition; you cannot return to mixed mode or Windows NT mode without rebuilding the entire system.

Several methodologies are available for a Windows 2000 migration. These are broadly based on two concepts: an in-place upgrade (henceforth known as an upgrade) or a restructure. An upgrade from a Windows NT environment to a Windows 2000–based infrastructure reflects exactly the current domain arrangement. A restructure consolidates the existing Windows NT resource and user domains to a more efficient arrangement of Active Directory domains and OUs. When combined, these two methodologies can create any of the following migration scenarios:

• An upgrade.
• An upgrade followed by a restructure.
• A restructure (or consolidation of Windows NT domains) and then an upgrade.
• A partial upgrade/partial restructure.
• A total restructure into a pristine Windows 2000 infrastructure. In many cases, it is preferable to construct a separate idealized Windows 2000 environment in isolation from the current environment. This is known as a pristine environment. Once created, you can migrate users and services from Windows NT in phases.

Depending on which book or resource you read or which guru you consult, you will find different perspectives on each methodology. Each methodology has a benefit and a risk or tradeoff. For example, a restructure to a pristine environment has less of an impact on the existing production environment and from this perspective will minimize the number of potential disasters. The tradeoff is that a restructure normally requires substantially more resources and design time depending on its size. An upgrade can potentially have less of an impact on the production environment because it can be performed immediately. The risk is that if the existing drivers don't function properly, you might find yourself in disaster recovery mode.

TIP

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When considering which methodology to use, don't get caught up in which one is the best. Instead, consider factors such as the size of your network, the impact on users and the business if a system is down for a day or several days, the number of objects in your domain to migrate, and so on. What's best for one organization might be totally inappropriate for another similar corporation.

An Upgrade

An upgrade—an in-place replacement of existing Windows NT servers with Windows 2000 servers—is shown in Figure 1.1.

Figure 1.1 An in-place upgrade

An upgrade doesn't entail changes to user or resource management. The in-place upgrade method is generally recommended for environments that meet the following criteria:

• Adequate existing structure. Your existing arrangement of users and resources meets your business needs and you want to maintain as many of the current settings as possible.
• Limited resources. You do not have the financial or human resources to deploy systems to adequately support a migration into a restructured environment. However, you still require many of the newer Windows 2000 features.
• Mission-critical applications. You have one or more mission-critical applications that will not function in a restructured environment.
• Size of enterprise. For a company with only two or three servers, an in-place upgrade is much faster once you've made the appropriate backups. Furthermore, this might be the correct procedure for several domains with a substantially large number of objects. It is simpler to upgrade first and restructure later rather than try to manage a large number of objects. For example, imagine how overloaded your help desk would be if 10 percent of 35,000 users called because of migration problems.

The main disadvantages of an in-place upgrade path include the following:

• The risk potential can be extremely high if a driver doesn't function under Windows 2000 or if an important factor (for example, an application dependency with another server) has been forgotten. Hence, you must make a verified backup before the upgrade.
• Old and possibly outdated files and registry settings will be retained and might cause problems later.

A Restructure

A restructure is the process whereby the user and resource domains present in a Windows NT deployment are mapped into an arrangement that uses the additional facilities provided by Active Directory, as shown in Figure 1.2.

Restructuring involves the movement of security principals between domains. You design a new Active Directory forest and then populate it with users, groups, and resources from the existing Windows NT environment. The result is a simpler structure in which management can be decentralized. For example, you can convert a Windows NT multiple-domain model into a single Active Directory domain with a consequent reduction in the number of trust relationships.

Figure 1.2 A restructure

Reasons to restructure include the following:

• Poor existing infrastructure. If your current business processes are restricted by a domain arrangement that you've outgrown or that was badly designed at the start, you should perform a restructure.
• Maximize migration deliverables. You can achieve many of the improvements that arise from a migration by moving to a well-designed Active Directory environment.
• No reuse. You don't plan to reuse your existing infrastructure.

Reasons not to restructure include the following:

• Insufficient management information. The roles and responsibilities for the final installation haven't been adequately defined. This might be because of an ongoing restructure or merger. In this situation, an upgrade followed by a restructure might be the best policy.
• Must stay in mixed mode. Some systems or management practices are required to remain as Windows NT systems. For example, if specific client applications are unable to access resources because they depend on Windows NT dynamic link libraries, you will be forced to retain the Windows NT environment.
• Insufficient budget and short-term hardware costs. The restructure will require a period of parallel running as the environment is migrated. This will necessitate additional server platforms during the upgrade period. You might not have sufficient budget for additional resources in the areas of support, training, and additional servers to perform an outright restructure. Instead, an upgrade followed by a later restructure might be advisable.

NOTE

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Many of the principal benefits of the move to Windows 2000 appear only when running in native mode. Therefore, consider a restructure in terms of when to do it rather than whether to do it.

An Upgrade and Restructure

An upgrade and restructure migration (see Figure 1.3) breaks the migration down into these two distinct phases, the first phase being the upgrade. Once the first phase has been proved to be successful the second phase involving the restructure can begin.

Figure 1.3 An upgrade followed by a restructure

Reasons to perform an upgrade and restructure include the following:

• To minimize the cost of the migration. An upgrade followed by a restructure requires fewer resources to implement. These resources might be deployed over a longer period of time.
• To be able to restore the original environment. If there are unknowns in the migration process that make it mandatory to be able to rewind the rollout at any point, you must stay in mixed mode until these issues have been resolved.

Reasons not to upgrade and restructure include the following:

• Timing considerations. The two-phased approach takes longer to plan and implement than an upgrade.
• Change fatigue. A stakeholder is anyone in the organization who has an interest in and is affected by the migration process. These stakeholders and those performing the migration will find it difficult to maintain morale and momentum if the migration appears to change the same object twice. For an example, consider a situation in which a Windows NT system policy affecting a user's desktop is changed when an upgrade moves to a group policy that has different or no desktop settings, and then the upgrade is followed by a restructure into a pristine environment that further affects the user's desktop depending on the group policies in effect in the pristine environment.

A Restructure Followed by an Upgrade

This type of migration is essentially an upgrade following a consolidation of domains. If you have several resource domains in your company consisting of only a few clients and objects, your upgrade will be far easier to manage if you first consolidate those resources into a smaller number of domains rather than upgrade every one. (See Figure 1.4.)

Figure 1.4 A restructure followed by an upgrade

A Partial Upgrade/Partial Restructure

A partial upgrade/partial restructure involves the creation of two distinct and separate environments, one in mixed mode and the other in native mode. With careful planning, the two can function on the same network infrastructure, and you can move users and resources from one to the other in a phased way until the legacy systems are either withdrawn or upgraded themselves.

Reasons for a partial upgrade and restructure include the following:

• Significant hardware rollout. If you're rolling out a significant upgrade to your systems, you could perform this task by installing Windows 2000 and implementing a parallel installation from the start. As the existing Windows NT machines are replaced by the newer Windows 2000 machines, the Windows NT systems can either be retired or upgraded.
• Significant need for pilot testing. If you're concerned about the viability of systems running on the native-based systems, you can run large pilot tests using existing data without causing a significant impact on your current production systems.
• High reliability requirements. If the systems must be highly reliable during the migration, you can maintain existing servers to provide backup support until the new installation has proved itself.

Reasons not to perform a partial upgrade/partial restore include the following:

• High cost. For much of the migration, you'll be duplicating systems, which will lead to extra costs.
• Hamper design. The need for parallel working might restrict the ultimate design because of factors such as dual namespace considerations.
• Difficulty duplicating components such as network infrastructure. Both the Windows NT and Windows 2000 environments might need to share some parts of the environment. In this case, the demands placed by the systems running concurrently on the same network could require extra bandwidth.

Practice: Scenario Analysis

In this practice, you'll analyze a set of migration scenarios and consider the best policy for the corporate installations described. For each one, you must determine the key considerations driving the migration, the optimal system arrangement under Windows 2000, and the deliverables to specify.

Migration Case Study 1

An advertising agency has offices in London, Paris, and New York. The Windows NT infrastructure includes a resource domain located at each of the offices and two account domains, one in London and one in New York. The migration has a limited budget and limited support staff. The migration is driven by a need for Microsoft Exchange Server 2000, a groupware messaging system that relies on the Windows 2000 Active Directory. The ad agency is currently in the middle of several large contracts that must not be disrupted.

Consider each of the following five migration methodologies and identify the advantages and disadvantages of each one for the company. Check your answers with those provided in Appendix A, "Questions and Answers."

A pure upgrade

An upgrade followed by a restructure

A restructure (or consolidation of Windows NT domains) and then an upgrade

A partial upgrade/partial restructure

A total restructure into a pristine Windows 2000 infrastructure

Migration Case Study 2

A manufacturing company, formed by the merger of an American and European company, has offices in Rome, Chicago, and Denver and manufacturing facilities in Hong Kong, Japan, and Texas. The company currently uses the multiple-master domain model that resulted from the creation of a two-way trust between the account domains from the original two companies and a large number of resource domains that have one-way trusts with their original account domains.

The company is concerned about the limitations of its structure hampering future development and the current difficulty of managing the system. The company is suffering from poor use of WAN bandwidth between sites, and it is currently setting up new corporate headquarters in Seattle.

Consider each of the following five migration methodologies and identify advantages and disadvantages of each for this company. Then check your answers in Appendix A.

A pure upgrade

An upgrade followed by a restructure

A restructure (or consolidation of Windows NT domains) and then an upgrade

A partial upgrade/partial restructure

A total restructure into a pristine Windows 2000 infrastructure

Lesson Summary

In this lesson, you learned the advantages and disadvantages of five different migration scenarios: an upgrade, a restructure, a consolidation and then an upgrade, an upgrade and then a restructure, and finally, a partial upgrade/partial restructure. These scenarios provide different advantages for the migration process as well as different tradeoffs.

In general, an upgrade is best where the underlying organization is sound and no requirement exists to make radical changes to it. Restructuring is preferable to rectify poor design and to maximize the benefits of installing Windows 2000. The ultimate aim should be a restructuring only when circumstances permit.