What are the fates of Adprep and Dcpromo?
Schema upgrades aren’t bothersome only to AD admins; they also irritate Microsoft's Customer Support Services (CSS), because confusion about the process is a high call generator. Further, adoption of many new AD-related and other features in a new OS was demonstrably slower if the feature depended on a schema upgrade because of the care (and resulting delay) associated with the process. As a result, one of the AD product group's goals for Windows Server 2012 was to make the process simpler, faster, and generally more pain-free than in previous versions. With Server 2012, Adprep has been integrated into the Active Directory Domain Services (AD DS) role installation process.Adprep is the utility—included in the OS installation media—that performs several crucial functions to upgrade AD to support that OS. The utility has three major options: /forestprep, /domainprep, and /rodcprep. The /forestprep option runs first, extending the AD schema with new object and attribute classes that the new AD version needs. The /domainprep option creates new well-known objects in AD, applies security changes, and miscellaneous other bits. Finally, /rodcprep makes forest-wide security changes to allow read-only domain controller (RODC) functionality.
Fear not, you old-school AD admins; you can still run Adprep manually from the \support\adprep folder of the Server 2012 installation disk, if you need to. But a difference from older Adprep versions is that there's no 32-bit version (Adprep32) of the utility. So, you can run Adprep only from a 64-bit version of Server 2008 or later.
You don't have to run Adprep from the schema master, but the Server 2012 server you're running the upgrade from (it doesn't have to be a DC) must have connectivity to the forest's schema master and the domain's infrastructure master. You can now also specify separate credentials for Adprep /forestprep (Enterprise Admins membership) or /domainprep or /rodcprep (Domain Admins membership) using the /user and /userdomain parameters. This gives you a great degree of flexibility in how you upgrade your forest and domains.
And even Dcpromo itself has disappeared. (If you try to run it, a dialog box appears, stating The Active Directory Domain Services Installation Wizard is relocated in Server Manager, and points you to a Technet article on how to install AD DS.) As the dialog box tells us, the process of installing the AD DS role on a server—thus making it a DC—has been moved to Server Manager. This is more than just a cosmetic move; the AD DS installation process has been completely re-engineered from the ground up. To make it less susceptible to errors, the process does a number of prerequisite checks before the promotion process ever begins, and either attempts to fix configuration errors or displays a message (in clear language, not developer-ese) describing the failure and suggesting steps to correct it. As with all other administrative tasks in Server 2012, everything you can do in the GUI can be done in PowerShell and vice versa. And you can export a PowerShell script that contains all the options you specified during the GUI installation, so you can reuse it on other DCs in your domain.
Every aspect of the Server 2012 DC installation and AD upgrade process has been examined and redesigned to be as seamless and low-effort as possible. In general, this is a very good thing; just be aware that it's so smooth and seamless that you'll need to guard against an unplanned forest and domain upgrade!