After my last column, I received several questions about planning for the number and size of the domain controllers you need when performing domain consolidation in Windows 2000. Windows NT 4.0 domains, with their limited number of directory objects and object attributes, are relatively straightforward. In Active Directory (AD), however, we have much more flexibility in deciding what types of objects to create and how much detail we will store as attributes for those objects. And increasingly, we'll have more AD-integrated applications, which will affect AD size and performance.

Fortunately, Microsoft has released a tool called AD Sizer (adsizer.exe) to help you estimate the size that your AD might grow to—an important consideration when designing a domain structure. AD Sizer also makes recommendations about the number of domain controllers and their hardware configurations. You can download the tool at the Microsoft Web site.

Once you download and install adsizer.exe, a folder appears in the Start menu's Programs group that contains the application and a Help document. When you start the application and choose File, New, an Active Directory Sizer Wizard launches that gathers information about your environment so that the tool can perform sizing calculations, as Screen 1 shows. AD Sizer asks you about the number of users and computers at your site, the types of objects that you plan to create in AD, whether you plan to use AD-integrated DNS, and about other factors that affect the directory's size. AD Sizer also asks about the number and types of concurrent logons, anticipated changes, and directory searches. The tool uses such information along with the CPU type and the acceptable processor utilization levels to help size your domain controllers and make recommendations about how many you need. AD Sizer even asks whether you plan to use Exchange 2000. If so, it makes adjustments to accommodate that application because it's AD integrated. As Microsoft introduces more AD-integrated applications, the company will continue to update AD Sizer. Before you use AD Sizer, Microsoft recommends that you check its Web site to make sure that you have the latest version.

After AD Sizer performs initial calculations based on the information that you provided, it gives you information to use for planning how many domain controllers you need and hardware configurations, as Screen 2 shows. At this point, you can add sites, move servers into sites, and create additional domains to more accurately reflect your environment. Such options let you experiment with different designs to determine which is the best for your environment.

AD Sizer is a great tool for planning your migration to AD and determining your hardware requirements for domain consolidation. I recommend that you use the tool to compare the costs of supporting an in-place upgrade of your current domain structure against the hardware costs of moving to one or fewer domains. The results of this comparison might help your company's number crunchers understand the benefits of taking the time to properly plan your migration to Win2K.