Active Directory Support Files
The ESE engine used by Active Directory is based on Microsoft's Jet database technology. Jet uses a b-tree file structure with transaction logs to ensure recoverability in the event of a system or drive failure.
When you promote a server to a domain controller, you select where to put the Active Directory files. The default path is in the boot partition under \Windows\NTDS. Generally, it is a good idea to put them on a separate volume from the operating system files to improve performance.
The following list contains the Active Directory support files and their functions:
This is the main AD database. NTDS stands for NT Directory Services. The DIT stands for Directory Information Tree. The Ntds.dit file on a particular domain controller contains all naming contexts hosted by that domain controller, including the Configuration and Schema naming contexts. A Global Catalog server stores the partial naming context replicas in the Ntds.dit right along with the full Domain naming context for its domain.
This is a transaction log. Any changes made to objects in Active Directory are first saved to a transaction log. During lulls in CPU activity, the database engine commits the transactions into the main Ntds.dit database. This ensures that the database can be recovered in the event of a system crash. Entries that have not been committed to Ntds.dit are kept in memory to improve performance. Transaction log files used by the ESE engine are always 10MB.
These are auxiliary transaction logs used to store changes if the main Edb.log file gets full before it can be flushed to Ntds.dit. The xxxxx stands for a sequential number in hex. When the Edb.log file fills up, an Edbtemp.log file is opened. The original Edb.log file is renamed to Edb00001.log, and Edbtemp.log is renamed to Edb.log file, and the process starts over again. ESENT uses circular logging. Excess log files are deleted after they have been committed. You may see more than one Edbxxxxx.log file if a busy domain controller has many updates pending.
This is a checkpoint file. It is used by the transaction logging system to mark the point at which updates are transferred from the log files to Ntds.dit. As transactions are committed, the checkpoint moves forward in the Edb.chk file. If the system terminates abnormally, the pointer tells the system how far along a given set of commits had progressed before the termination.
Res1.log and Res2.log.
These are reserve log files. If the hard drive fills to capacity just as the system is attempting to create an Edbxxxxx.log file, the space reserved by the Res log files is used. The system then puts a dire warning on the screen prompting you to take action to free up disk space quickly before Active Directory gets corrupted. You should never let a volume containing Active Directory files get even close to being full. File fragmentation is a big performance thief, and fragmentation increases exponentially as free space diminishes. Also, you may run into problems as you run out of drive space with online database defragmentation (compaction). This can cause Active Directory to stop working if the indexes cannot be rebuilt.
This is a scratch pad used to store information about in-progress transactions and to hold pages pulled out of Ntds.dit during compaction.
This file is used to initialize the Ntds.dit during the initial promotion of a domain controller. It is not used after that has been accomplished.