Metabase Update Service
Metabase update service, also referred to as the directory service/metabase synchronization process, or DS2MB (because this process is implemented in DS2MB.dll) is a component in Exchange Server 2003 that is used to synchronize several Exchange configuration settings in Active Directory with counterpart settings in the IIS metabase. The function of DS2MB is to replicate configuration information from Active Directory to the local IIS metabase.
The DS2MB process copies entire subtrees from Active Directory, without changing the shape of the subtree. This is a one-way write from Active Directory to the metabase; the metabase never writes to Active Directory. The DS2MB process does not add or compute any attribute when copying. The paths in the metabase are called keys. Properties can be set at each key, and each property can have attributes that customize that property. All identifiers that are present in the directory service image of the subtree are required in the metabase, including identifiers such as KeyType. In addition, the Relative Distinguished Name of the object in the directory is mapped directly to the key name in the metabase.
The metabase update is a subprocess that is launched when System Attendant is started. The operation of SMTP, POP3, IMAP4, Outlook Web Access and Outlook Mobile Access are all dependent on the replication by DS2MB. DS2MB registers with the config domain controller after startup, enabling the config domain controller to notify DS2MB of any changes that are made to the Exchange configuration. This notification occurs within 15 seconds of the change. As soon as the change is replicated to the configuration domain controller, the change should be replicated to the metabase by DS2MB. DS2MB tracks changes to directory objects based on update sequence numbers (USNs).