Active Directory maintains a multi-master database to store schema information, configuration information, and domain information. Normally, when we say database, first thing which comes to our mind is a software like Microsoft SQL, MySQL, or Oracle. But here it's quite different. Active Directory database uses the Extensible Storage Engine (ESE), which is an indexed and sequential access method (ISAM) technology.

Here, a single system works as the client and server. It uses record-oriented database architecture, which provides extremely fast access to records. ESE indexes the data in the database file. This database file can grow up to 16 terabytes and hold over 2 billion records. Typically ESE is used for the application which requires fast structured data storage. ESE is used for many other Microsoft applications including Microsoft Exchange, DHCP, FRS, and so on.

As the part of the domain controller installation process, it creates the database under C:WindowsNTDS unless we select a custom path. It is recommended to use separate partition/disk with higher speed to increase the database performances as well as the data protection:

In this folder, we can see few different files. Out of those, the following files are important.