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Preparing for Windows Server 2012 : Planning for Windows Server 2012 (part 1) - Migration scenarios

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The success of an infrastructure-migration project depends on careful planning combined with meticulous execution. You need to start by defining the scope of the project so that you know where you want to end up. Then you need to lay out a project plan that involves pilot testing to familiarize yourself with the new platform and to identify any potential issues that might arise during the migration process. A thorough assessment of your existing environment is also necessary to ensure there are no surprises coming. A methodology needs to be developed to migrate existing servers and roles. Finally, once the migration is underway, continued testing needs to be performed to ensure everything is happening as planned.

1. Migration scenarios

Migration projects involving servers can be categorized in a number of ways, depending on whether you are deploying a new infrastructure, upgrading or consolidating an existing infrastructure, or implementing a new infrastructure model such as cloud computing. In addition, migrations can differ depending on whether or not you are migrating your entire infrastructure or only portion of it; whether you plan on re-using existing hardware or moving to new hardware; whether your environment is managed or unmanaged; whether your existing infrastructure is large or small, centralized or distributed, heterogeneous or homogeneous; and many other factors.

With so many different ways of envisioning and scoping infrastructure-migration projects, it’s obvious that there is no single approach to how such projects should be planned and executed. However, there are some steps and considerations that are common to all migration projects, and being aware of such best practices and implementing them can help ensure the project’s success.

I’ll begin by describing the following six possible migration scenarios for organizations that want to take advantage of the new features and capabilities found in Windows Server 2012:

  • Greenfield

  • Forest upgrade

  • Mixed environment

  • Server consolidation

  • Private cloud

  • Public cloud

Note that other migration scenarios are also possible—for example, by combining two or more of the following scenarios to create hybrid scenarios.


In terms of infrastructure, a greenfield deployment is one where no infrastructure currently exists. For example, let’s say that Contoso, Ltd. is a new company starting up that needs an on-premises infrastructure deployed for its rapidly growing workforce. A greenfield deployment of an infrastructure based on Windows Server 2012 might include steps like these:

  • Designing, acquiring and implementing the underlying network infrastructure of switches, routers, access points, and other networking hardware.

  • Designing the Active Directory environment using the guidelines and best practices found in the AD DS Design Guide at

  • Purchasing system hardware that has been certified for Windows Server 2012.

  • Performing a pilot deployment to determine whether the planned infrastructure will meet your business needs and to anticipate any possible problems that might arise during the rollout.

  • Rolling out your production infrastructure using whatever deployment tools you’ve decided to use. 

The main advantage of a greenfield migration is that it gives you the opportunity to get it right from the start. On the other hand, businesses are always evolving and are rarely static, so even if you carefully plan for future growth you might still be faced with challenges in evolving your infrastructure to address events such as mergers, acquisitions, and spinoffs of business units. And as a reality check, most readers of this Training Guide who are looking to upgrade their job skills are likely to be working at companies that have one or more existing Active Directory forests in place and are contemplating migrating them to Windows Server 2012, which is what the next migration scenario is about.


REAL WORLD Migration from scratch

In one sense, it might seem strange to call a greenfield deployment a “migration.” After all, how can you migrate from something that didn’t previously exist? However, the underlying IT infrastructure of most new businesses generally isn’t one that starts from scratch but instead evolves, rapidly or slowly, until a decision is made to settle on a specific infrastructure model and implement it using a formally agreed-upon process.

For example, the founders of Contoso, Ltd. might have started up their business in the garage of one of their homes and used free Google Apps running on Apple MacBook laptops via a neighborhood WiFi connection to do all their initial planning, accounting, and communications. Once they leased offices and hired several dozen employees, however, they might decide that it makes business sense for them to deploy an infrastructure that centralizes the management and ensures the security of their IT resources. Depending on how they foresee their business evolving, they might decide to either deploy a new Active Directory forest on-premises, implement a private cloud solution, or use a public cloud service provider.

Forest upgrade

Administrators of Active Directory environments have traditionally been cautious, or even paranoid, about performing schema upgrades using the Adprep.exe command-line utility. With the release of each new version of Windows Server comes a new schema version as well, and in the past, the task of introducing domain controllers running the new version of Windows Server into your existing Active Directory environment has required that you first prepare your forest by upgrading the schema. The reluctance that administrators have toward performing such upgrades is based largely on three concerns:

  • The process of upgrading a forest schema using Adprep was often a cumbersome one on previous versions of Windows Server and involved using a variety of different credentials to log on to specific domain controllers, copy Adprep files, and run Adprep from the command line with various parameters. The more complex the process, the greater the chance is of an error occurring.

  • There was the possibility that something might go wrong during the schema upgrade process, resulting in a corrupt forest that requires you to perform a forest recovery, which can be a difficult and time-consuming process.

  • There was the possibility that the schema upgrade might go off well but result in side effects, such as enterprise applications that break and no longer function properly.

The recommended approach to avoiding such problems is to create a test environment that mirrors your production environment in terms of its Active Directory schema, network services, and business applications. By upgrading the schema of your test forest using Adprep, you can then better anticipate any problems that might arise when you upgrade the schema of your production forest. 

Clearly, these are not trivial concerns when your job as administrator is potentially at stake. So before you perform a forest upgrade, you need to be well prepared—for example:

  • You need to understand the schema upgrade process and its possible impact on your environment.

  • You need to have a forest recovery plan in place as a backup solution for your worst-case scenario.

With Windows Server 2012, however, Microsoft has endeavored to alleviate many of the concerns administrators often have about performing forest upgrades. For example:

  • Adprep functionality is now integrated into the Active Directory Domain Services (AD DS) installation process. In most cases, this now eliminates the need to separately run Adprep prior to introducing domain controllers running the new version of Windows Server.

  • The new AD DS installation process includes prerequisite validation to identify potential errors before installation begins. For example, if the installation process determines that adprep /domainprep needs to be run to prepare the domain, verification is done first to ensure that the user who initiated the process has sufficient rights to perform the operation.

  • The Windows Server 2012 forest functional level does not add any new features to a forest and ensures only that any new domain added to the forest will automatically operate at the Windows Server 2012 domain functional level.

  • The Windows Server 2012 domain functional level adds only one new feature to a domain. This new feature relates to Dynamic Access Control (DAC) and therefore is unlikely to affect any existing applications and services in your environment.

Despite these improvements to performing schema upgrades and raising forest and domain functional levels, careful planning and due care should be performed when completing these tasks. 


Forest upgrades and functional levels

After upgrading your schema, you might want to raise your forest and domain functional levels. As a best practice, follow these practices:

  • Before changing your forest functional level, take at least one domain controller offline from each domain in your forest.

  • Before changing the domain functional level of any domain, take at least one domain controller offline from the domain.

In both cases, you should make sure that the domain controllers you take offline do not hold any flexible single master operations (FSMO) roles in the forest or domains.

Keep the domain controllers offline for 48 to 72 hours after changing functional levels; if no issues are found, you can return the offline domain controllers to service. If issues are discovered, however, you can use your offline domain controllers as the source for rebuilding servers if a rollback to a previous functional level is required.

Mixed environment

As you saw in the previous migration scenario, existing businesses that want to take advantage of the new capabilities of Windows Server 2012 can do so without ripping out their infrastructure and replacing it with a new one. All they need to do is introduce servers running Windows Server 2012 into their environment and promote them as domain controllers. Doing this automatically upgrades the schema, and administrators can raise the forest and domain functional levels to Windows Server 2012 with minimal fear of it having a negative impact on their existing applications and services. Of course, regardless of this, you should still be sure to first test your schema upgrade and functional level changes in a test environment that mirrors your production environment just to make sure there will be no issues that might impact your business.

But some new features of Windows Server 2012 can also be implemented into existing Active Directory environments without making significant changes to the existing forest, such as upgrading the schema or raising the forest or domain functional levels. An example where this might be done is when deploying new DHCP servers to take advantage of the new DHCP failover feature of Windows Server 2012 that ensures continuous availability of DHCP services to clients.

The introduction of member servers running Windows Server 2012 into an Active Directory forest based on an earlier version of Windows Server results in a mixed environment of servers running different versions of Windows. By not introducing new domain controllers in Windows Server 2012, administrators can continue to manage their environment using existing tools and processes. Although this seems like a simpler and less risky approach than upgrading your forest as described previously, there are several disadvantages to following this migration approach:

  • Some new features and capabilities of Windows Server 2012 can be implemented only when your Active Directory environment includes domain controllers running Windows Server 2012. These features might not work at all, or have only limited functionality, when your Active Directory schema hasn’t been upgraded to Windows Server 2012. In general, information about such limitations might be buried in the TechNet Library documentation for Windows Server 2012, which means you need to do some research before you try deploying Windows Server 2012 member servers with roles and features installed in your existing Active Directory environment.

  • Some of the server administration tools built into Windows Server 2012 and included in the Remote Server Administration Tools (RSAT) for Windows 8 have limited or no functionality when managing servers running previous versions of Windows Server. Or you might have to install additional updates on servers running previous versions of Windows Server in order to manage them using the Windows Server 2012 server administration tools or RSAT for Windows 8. 

So while rolling out a few Windows Server 2012 member servers with a few roles and features installed might seem like a good idea, and less risky than performing a forest upgrade, the gains you experience from following this approach might not balance against the effort involved.

Server consolidation

Server consolidation involves using virtualization to consolidate multiple server workloads onto a single virtualization host. Although server consolidation can help an organization improve server utilization and reduce costs, it isn’t generally considered a migration scenario.

With the greatly increased scalability of the Hyper-V role in Windows Server 2012, however, some businesses might be able to migrate much or even all of their existing Active Directory infrastructure based on a previous version of Windows Server and run it on a cluster of Hyper-V hosts running Windows Server 2012. In other words, they can migrate their existing physical servers into a virtual environment. 

Private cloud

Cloud computing provides organizations with new options to increase efficiencies while reducing costs. The traditional data-center approach, where the organization deploys and manages its own Active Directory infrastructure on-premises, has known stability and security, but the infrastructure servers involved often run at less than 15 percent utilization. Virtualizing the data center by using server consolidation can increase utilization, reduce cost, and simplify management, but this approach lacks the elasticity to rapidly meet changing demands as your business grows or experiences market changes.

Cloud computing can simplify management and reduce cost even further while providing elasticity and the perception of infinite capacity for the IT services your business uses. Cloud resources are pooled so that they can be allocated on demand as the needs of the business grows or shrinks. If additional resources are needed, they can be provisioned without the need for extensive planning and testing beforehand.

Cloud computing can be provisioned according to three possible service models:

  • Software as a Service (SaaS) The cloud is used to deliver an application to multiple users, regardless of their location or the type of device they are using. Compare this model with the more traditional approach of deploying separate instances of applications to each user’s PC. This approach is typically is used to deliver cloud-based applications that have minimal need for customization. Examples include email, Customer Relationship Management (CRM), and productivity software. The advantages of this approach are that application activities can be managed from a single central location to reduce cost and management overhead. An example of a SaaS offering from Microsoft is Office 365, which provides users with secure access from anywhere to their email, shared calendars, instant messaging (IM), video conferencing, and tools for document collaboration.

  • Platform as a Service (PaaS) The cloud is used to deliver application execution services, such as application run time, storage, and integration for applications designed for a prespecified, cloud-based architectural framework. This allows you to develop custom cloud-based applications for your users with secure access from business, which you can then host in the cloud so that your users can access them from anywhere over the Internet. PaaS also lets you create multitenant applications that multiple users can access simultaneously. With support for application-level customization, PaaS allows integration with your older applications and interoperability with your current on-premises systems, although some applications might need to be recoded to work in the new environment. An example of a PaaS offering from Microsoft is SQL Azure, which allows businesses to provision and deploy SQL databases to the cloud without having to implement and maintain an in-house Microsoft SQL Server infrastructure.

  • Infrastructure as a Service (IaaS) The cloud is used to create pools of computer, storage, and network connectivity resources, which can then be delivered as cloud-based services billed on a per-usage basis. IaaS forms the foundation for the other two cloud service models by providing a standardized, flexible, virtualized environment that presents itself as virtualized server workloads. In this approach, the organization can self-provision these virtualized workloads and customize them fully with the processing, storage, and network resources needed and with the operating system and applications needed. The organization is relieved of the need to purchase and install hardware and can simply spin up new workloads to meet changing demand quickly.

In the context of Windows Server 2012 migration scenarios, the cloud service model under consideration here is the IaaS model, which can be implemented by using the Hyper-V role of Windows Server 2012 together with Microsoft System Center 2012 SP1. When IaaS is implemented in such a way that the customer controls the cloud, the solution is called a private cloud. There are several ways a private-cloud solution can be implemented by an organization:

  • By having the customer build and host the private cloud in its own datacenter using Windows Server and the System Center family of products

  • By having the customer purchase a dedicated private cloud appliance with Windows Server and System Center preinstalled and configured

  • By having a partner company host the customer’s private cloud

Migrating an organization’s existing Active Directory infrastructure into a private-cloud sourcing model can be straightforward or complex, depending on a number of different factors. Because of this, it’s useful to enlist a Microsoft partner to help you design and implement a solution that meets the needs of your organization. If you want to explore the private-cloud option further, there are several places you can start:

  • You can download private-cloud evaluation software from Microsoft and deploy it in a test environment. At the time of this writing, this offering uses Windows Server 2008 R2 SP1 and System Center 2012, but by the time you read this, Microsoft might have upgraded the offering to Windows Server 2012 and System Center 2012 SP1. 

  • You can purchase an IaaS private cloud with a prevalidated configuration from server partners in the Microsoft Private Cloud Fast Track program. These offerings combine Microsoft software, consolidated guidance, validated configurations from original equipment manufacturer (OEM) partners, and other value-added software components.

  • You can use the Microsoft Pinpoint site to find a partner in the Microsoft Private Cloud Service Provider Program who can host a dedicated private cloud for your organization. 

Public cloud

The private cloud is one of several cloud-sourcing models that organizations can consider. Another approach is using a public cloud, which is where a hosting provider maintains a shared cloud that provides a pool of services that can be used by multiple customers. It’s important in such a model that each customer’s environment be fully isolated from that of other customers to ensure security, and Windows Server 2012 includes new virtualization technology that enables secure multitenancy for hosting scenarios like this.

Public-cloud hosting providers generally focus on delivering SaaS solutions that allow them to deliver applications to customers so that the customer can focus on solving business problems instead of managing infrastructure.

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