User Account Database Fails to Shrink after Deleting Accounts

The information in this article applies to:

• Microsoft Windows NT operating system version 3.1
• Microsoft Windows NT Advanced Server version 3.1
• Microsoft Windows NT Workstation versions 3.5, 3.51, and 4.0
• Microsoft Windows NT Server versions 3.5, 3.51 and 4.0

SUMMARY

If a large number of users are added to a Windows NT User Account Database, and later deleted, the size of the User Account Database or Security Account Manager (SAM) does not shrink in size.

Windows NT does not have a mechanism to compress this empty space, but it is reclaimed when new user or group accounts are created. When the Windows primary domain controller synchronizes the SAM with the backup domain controllers, the new records, or changes in existing records are sent. The SAM is located in %SYSTEMROOT%\SYSTEM32\CONFIG\SAM.

If the SAM file grows too large, additional memory and PagedPoolSize is needed to load the file at system boot, and to load applications such as User Manager. For guidelines and additional information, please see the following article in the Microsoft Knowledge Base:

   ARTICLE-ID: Q130914
   TITLE     : Number of Users and Groups Affects SAM Size of Domain

MORE INFORMATION

Although Windows NT has no built-in method of compressing the SAM database, there are three methods that can be used to effectively compress the SAM on a certain domain controller. The compressed SAM is NOT replicated to backup domain controllers since only new records, or changes in the records are replicated. Therefore, measures will need to be applied at each Domain Controller.

Method 1: This method must be performed on a backup domain controller. Use the ERD (Emergency Repair Disk) and select "Inspect registry files." When prompted, choose "SECURITY (SecurityPolicy) and SAM (User Accounts Database). This replaces the large SAM with the original one that was created when Windows NT was installed on this machine. This requires the Administrator password that was used when Windows NT was installed, or when RDISK -s was last used. After replacing the SAM, synchronize with the primary domain controller. Promote a backup domain controller to become primary domain controller to apply the above fix to the original primary domain controller.

Method 2: This is the most invasive method, and requires any services or applications to be reinstalled. Install Windows NT onto the same machine of a backup domain controller as a "New Install".

This overwrites the large SAM, creating a new file and downloading the accounts from the primary domain controller. This can be done to all of the backup domain controllers. To re-install the primary domain controller, promote a backup to primary, and perform the same operation.

Method 3: This method can be done on a backup or primary domain controller. This method uses the utilities REGBACK and REGREST from the Windows NT Resource Kit. Using REGBACK will copy the records from the SAM into a new file. Restoring the SAM copies this new file over the old SAM. You must reboot the computer after using REGREST to have the restore take effect.

NOTE: After you back up the SAM using REGBACK, you can compare the two files and determine the size of free space or extraneous information.

The net result is a compressed SAM database. As an example, the following command lines could be used. These assume the BACKUP directory already exists on drive C, and Windows NT is also installed on drive C (Windows NT and the BACKUP directory must reside on the same logical disk):

   C:\>regback c:\backup\sam.bak machine sam

   -or-

   C:\>regrest c:\backup\sam.bak c:\backup\sam.old machine sam