The Active Directory database is where all information relating to the directory is stored, including domain objects and attributes, schema, configuration, and global catalog information if applicable. As such, you must have an awareness of how the database works, as well as how it can be maintained. This includes knowing how to do a backup/restore, defragmentation, as well as how to move the database.
The Active Directory database is referred to as a transactional database, which means that every change to the database is treated as an individual transaction. The transactional nature of the database helps maintain integrity in the event of a failure. The Active Directory database is actually made up of a number of files that you need to be aware of:
Ntds.dit – this is the actual AD database file, where all objects are stored. By default you will find this file (and the others mentioned here) in the %systemroot%\NTDS folder.
Edb*.log – these files are transaction logs. Before any update is written to the database, it is first written to the transaction log. Each edb.log file is 10 MB in size. By default Windows 2000 uses circular logging, meaning that once full, the log file begins overwriting the oldest changes. If circular logging is turned off once the log files are full they are renamed ebdxxxxx.log, with xxxxx representing the number of the file starting at 00001.
Edb.chk – this is a checkpoint file, used by AD to track which changes have been written to ntds.dit. This is used for recovery purposes. For example, if a domain controller crashed and information had not yet been written to the database, the checkpoint file would server as the marker/pointer as to what from the log file still needs to be written to the database.
Res1.log and Res2.log – These are reserved log files, 10 MB each. Their purpose is to allow Active Directory to continue to log changes, in the event that all disk space in filled. As such, these 20 MB of files are actually just empty files reserving space, and are not used unless needed.
Remember from our earlier look at installing Active Directory that Microsoft recommends placing the log files and database on separate disks for best performance.