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What Is the Data Store?

Updated: March 28, 2003

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2, Windows Server 2008, Windows Server 2008 R2

In this section

In Active Directory, the data store contains database files and processes that store and manage directory information for users, services, and applications. A copy of the data store runs on each domain controller in the forest. The Active Directory data store is often referred to as the directory.

In Windows 2000 Server and Windows Server 2003, the directory service is named Active Directory. In Windows Server 2008 and Windows Server 2008 R2, the directory service is named Active Directory Domain Services (AD DS). The rest of this topic refers to Active Directory, but the information is also applicable to Active Directory Domain Services.

The Business Need

Organizations generate and store data about many different kinds of entities (computers, users, services, and so on) that exist in their information technology (IT) infrastructure. Historically, organizations maintain this information in multiple locations and formats. For example, an organization might store employee information in a human resources database, application data in an application-specific database, Quality of Service (QoS) rules on routers, and security information (user name and password) on a network server. Storing, managing, and making available many disparate data sets is expensive and time consuming.

The Data Store Solution

The Active Directory data store solves the problem of managing disparate data sets across an organization. The data store is a single, general-purpose database that can hold many types of data and distribute that data to users anywhere on the network. The following figure illustrates the use of the Active Directory data store as a single, general-purpose database for all of an organization’s data.

Data Store

Data Store

The Active Directory data store achieves the following major design goals:

  • To provide distributed access to the directory by users and applications, a copy of the data store resides on all domain controllers in a domain or forest.

  • To provide standard interfaces for accessing data, the data store includes a Lightweight Directory Access Protocol (LDAP) interface and a Messaging API (MAPI) interface.

  • To support quick searches of directory data, the data store includes efficient query and index mechanisms.

  • To ensure scalability, the data store uses a hierarchical, or tree, model that supports partitioning. The data store also ensures scalability by automatically managing database growth and increasing the database file size when necessary.

  • To support both full and incremental restoration of data, the data store uses a transactional model, logging uncommitted transactions in log files.

  • To ensure data consistency, the data store enforces a set of extensible data type and format constraints, called the schema.

Data Store Scenarios

Active Directory is required for the deployment and operation of Windows Server 2003 and later domains and forests. The data store is a key and required part of any Active Directory deployment. Therefore, the data store exists in any Windows Server 2003 and later domain or forest. Use of the data store can be further delineated into two main scenarios, based on the type of data that is stored. These scenarios are the network operating system (NOS) directory scenario and the NOS and application directory scenario.

NOS Directory Scenario

In the NOS directory scenario, an organization uses the data store only for storage of NOS-related information, including information about users, computers, services, printers, and so on. This scenario applies to organizations that are not running directory-enabled applications (applications that can communicate with and store data in a directory data store) or to organizations that are using a different directory data store than Active Directory for storing application data. In this scenario, you can manage the data in the data store by using the command-line and graphical user interface (GUI) tools that are provided with Windows Server 2003 and later.

NOS and Application Directory Scenario

In the NOS and application directory scenario, directory-enabled applications that are not a part of the NOS use the data store to hold application-specific data. Examples of directory-enabled applications include messaging, customer relationship management (CRM), enterprise resource planning (ERP), and document management applications. In this scenario, the schema (the set of rules that define the type and formatting of data) is generally extended to include data definitions that are specific to the directory-enabled applications that use the data store.

Directories and Databases

In the context of directory services, questions often arise regarding the differences between directories and databases. The Active Directory data store shares many aspects in common with databases, including the storage of data in rows and columns and the use of a hierarchical data model.

A directory differs from a database primarily in its intended use. A directory is optimized for read operations, while a database is optimized for write and change operations. Therefore, any data that is read many more times than it is written or modified is a good candidate for storage in a directory.

A directory also typically differs from a database in the protocols that it uses to access information in the data store. A directory, such as Active Directory, is most often accessed with LDAP. A database is most often accessed with an interface such as Structured Query Language (SQL).

Data Store Dependencies

The Active Directory data store depends on several related technologies and resources for its proper functioning. The following sections describe these technologies and resources.


The data store requires a disk volume that is formatted with the NTFS file system. NTFS is more powerful than FAT16 or FAT32, and NTFS includes features that are required for hosting Active Directory. For more information about NTFS, see “NTFS Technical Reference.”

Network Connectivity

So that users and computers can access the data store, and to support replication of the data store between domain controllers, network connectivity with TCP/IP is required. For more information about networking and TCP/IP, see “TCP/IP Technical Reference.”

Active Directory Replication

Except for very small networks, directory data must reside in more than one place on the network to be equally useful to all users. Through the process of replication, Active Directory maintains copies, or replicas, of the data store on each domain controller in the forest, which helps to ensure data availability and performance for all users. For more information about replication, see “Active Directory Replication Model Technical Reference.”


The File Replication service (FRS) is a process that is associated with the Distributed File System (DFS). FRS is used by Active Directory to replicate the system volume (SYSVOL) between domain controllers. SYSVOL holds certain kinds of Active Directory information, including Group Policy objects (GPOs) and scripts. For more information about FRS, see “FRS Technical Reference.”

Disk Space

There are no practical limits to the number of objects that can be stored in the Active Directory data store. The Active Directory directory database has been tested for up to 40 million objects. Performance tests show logon performance for a single LDAP client to be the same with 10,000 objects, 100,000 objects, and 1 million objects; that is, the directory service does not slow measurably when the size of the database increases.

The minimum free disk space requirements for the directory database and log files depend on the size of the database. On partitions that hold the database only (and not the database log files), free disk space must not fall below the greater of 20 percent of the disk space that is consumed by the database or 500 megabytes (MB). On disk volumes that hold the database and the database log files, free disk space must not fall below the greater of 20 percent of the combined size of the Ntds.dit and log files or 1 gigabyte (GB). For more information about the Ntds.dit and log files, see “How the Data Store Works.”

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