Restoring a Domain Controller
One of the benefits of Active Directory is built-in redundancy. When you lose a single domain controller, the impact can be insignificant. With many services, such as DHCP, the architecture dictates a dependency on a specific server. When that server becomes unavailable, clients are impacted. Over the years, failover or redundancy has been built into most of these services, including DHCP. With Active Directory, the architecture is built around redundancy. Clients are not dependent on a single DC; they can failover to another DC seamlessly if a failure occurs.
When a failure does occur, you should ask yourself several questions to assess the impact:
- Is the domain controller the only one for the domain?
This is the worst-case scenario. The redundancy in Active Directory applies only if you have more than one domain controller in a domain. If there is only one, you have a single point of failure. You could irrevocably lose the domain unless you can get that domain controller back online or restore it from backup.
- Does the domain controller have a FSMO role?
The five FSMO roles outlined in Chapter 2 play an important part in Active Directory. FSMO roles are not redundant, so if a FSMO role owner becomes unavailable, you’ll need to seize the FSMO role on another domain controller. Check out the FSMO recovery section later in this chapter for more information.
- Is the domain controller a Global Catalog server?
The Global Catalog is a function that any domain controller ...