Of the three components responsible for Exchange Server LDAP queries to Active Directory, DSAccess is probably the most critical. The DSAccess service's primary job is to discover the Active Directory topology, and then provide that information to Exchange Server.
The DSAccess service is dynamic and completely automated. Once every 15 minutes, it analyzes your Active Directory topology looking for any changes since the last discovery poll.
More specifically, the DSAccess service is looking for:
- Changes to the site structure
- The addition or removal of domain controllers
- Changes in domain controller placement
- Available global catalog servers
Technically speaking, the DSAccess service is part of Exchange Server; it is contained within the DSACCESS.DLL file.
Instead of collecting information through an LDAP query against AD, Microsoft chose to break DSAccess out into a separate service in order to increase efficiency. Each time DSAccess queries are performed, the information is stored in the DSAccess cache. This means Exchange Server doesn't have to perform a fresh query every time it needs to access a domain controller, or every time a Microsoft Outlook client needs to access a global catalog server.
DSAccess can dynamically detect domain controller and global catalog failures. When it detects a failure, it helps Exchange to fail over to an alternate domain controller or global catalog server (assuming that one exists), thus reducing potential downtime.
The DSAccess service also maintains a second cache to store the results of LDAP queries. That way, if another user makes a similar request, Exchange can save time by just returning the cached query result.
TUTORIAL: HOW EXCHANGE PERFORMS ACTIVE DIRECTORY LDAP QUERIES
Part 1: How the DSAccess service works in Exchange and Active Directory
Part 2: How the DSProxy service works in Exchange and Active Directory
Part 3: How the SMTP categorizer works in Exchange and Active Directory
|ABOUT THE AUTHOR:|
| Brien M. Posey, MCSE
Brien M. Posey, MCSE, is a Microsoft Most Valuable Professional for his work with Exchange Server, and has previously received Microsoft's MVP award for Windows Server and Internet Information Server (IIS). Brien has served as CIO for a nationwide chain of hospitals and was once responsible for the Department of Information Management at Fort Knox. As a freelance technical writer, Brien has written for Microsoft, TechTarget, CNET, ZDNet, MSD2D, Relevant Technologies and other technology companies. You can visit Brien's personal Web site at www.brienposey.com.