Microsoft Knowledge Base Article 315131 contains the following summary:
This step-by-step article describes how to manage Active Directory files from the command line and describes the main directory file.
Microsoft Windows 2000 Directory Service is implemented on top of an indexed sequential access method (ISAM) table manager.
This table is the same table manager that is used by Microsoft Exchange Server, the file replication service, the security
configuration editor, the certificate server, Windows Internet Name Service (WINS), and other Windows 2000 components.
The version of the database that Windows 2000 uses is called extensible storage engine (ESENT).
ESENT is a transacted database system that uses log files to support rollback semantics to ensure that transactions are committed to the database. Ideally, you should locate data and log files on separate drives to improve performance and to support recovery of the data if a disk fails.
The data file is called Ntds.dit. You can use the commands on the Files menu in Ntdsutil to manage the Directory Service data and log files.
ESENT provides its own tool called Esentutl.exe that you can use for certain database file management functions. Esentutl.exe is installed in the Winnt\System32 folder. Several of the Ntdsutil file management commands initiate Esentutl, which reduces the need to learn that tool's command-line arguments. If Ntdsutil initiates Esentutl, Esentutl generates a separate window that is configured with a large history so that you can scroll back to see all of the Esentutl progress indicators.
Windows 2000 Directory Service opens its files in exclusive mode. This means the files cannot be managed while the server is operating as a domain controller.