DSAccess - Directory Service Access

What is DSAccess?
DSAccess is a component that optimizes the communication between Active Directory and components within exchange server.

For example, Components such as Information Store and message categorizer.

Exchange components that needs to interact with active directory uses DSAccess to retrieve information instead of directly communicating with Domain Controller or Global Catalog servers.

DSAccess is also helpful for better system performance as it maintains a cache which helps in reducing LDAP queries that exchange server components does on active directory and thus load is reduced on both domain controllers as well as global catalog servers.

Note: Global Address List (GAL) queries from Microsoft Outlook client does not use this cache.

The system Attendant service is responsible for initializing DSAccess which is in form of a DLL file i.e., DSACCESS.DLL. There are also two more dll's associated which are DSCMGS.DLL and DSCPERF.DLL.

Lets say, we want to see which processes are using DSACCESS.DLL. for this we will be using tasklist.exe (windows 2003 and XP) from command prompt.
tasklist -m dsaccess.dll
This will give you output similar as shown below.
 
DSAccess also have another important task to do, and that is "Discovery Process". In this discovery process DSAccess determines the complete active directory structure and accordingly chooses domain controller and global catalog servers that can be used by exchange.

To see which domain controller and global catalog is being used by DSAccess, we need to open ESM (exchange system manager) and drill down to server, then open the properties page of server and go to Directory Access tab.
 
Note: This is available only if Exchange 2003 SP2 is installed. In prior versions you will need to use DSADIAG.EXE to get the list of domain controllers and global catalogs that are being used by DSAccess.