Fallback Plans and Failover Procedures

When planning a migration, how to migrate is not always the most import component to consider. Sometimes understanding the best approach and tasks involved to recover from a failed migration can be just as important as the migration tasks themselves .

The following sections review common areas to consider and tips that can allow administrators the capability to undo tasks in certain migration scenarios.

Test All Migration Scenarios

It is best practice to test all migration scenarios in an isolated lab environment prior to attempting a live migration.

Simple Methods to Recovering the SAM Database

When performing an in-place upgrade of a Windows NT 4.0 domain, or even when migrating domains, corruption of SAM databases or unrecoverable failures of the Windows NT Primary Domain Controller (PDC) and Backup Domain Controllers (BDCs) can occur. These cases require a full recovery of the original source domain's SAM database.

One method to recovering the original NT source domain is to create a backup Domain Controller that can be isolated from the production domain for recovery purposes in case of an unrecoverable failure.

Installing an additional Windows NT Back Up Domain Controller on the source domain creates a copy of the SAM database, which can then be pulled of the network and shut down. To recover the SAM database in case of a failure, the recovery server can simply be turned on and promoted to the domain's new primary domain controller, providing a complete copy of the original SAM database.

Recovering from Failed Account Migrations

When migrating accounts such as desktops and user accounts, one challenge administrators face is how to recover if a migration were to fail. The simplest method is to understand and leverage the options available with the Active Directory Migration Tool (ADMT).

Using the Active Directory Migration Tool to migrate accounts enables you to preserve the original account in a disabled state within the source domain, while at the same time creating a new account in the new Active Directory target domain. In the case of a failed migration, administrators can simply enable the original account, providing immediate access to network resources for the user account that failed to migrate. Review the options and settings available for account migration in Figure 14.2 to determine the best method for migrating accounts based on the migration's specific requirements.

Figure 14.2. ADMT user migration options.