The Data Access Server (DAS) is part of the Business Logic layer. Most requests for data from the database and all requests to insert data into the database go through the DAS. The DAS links Consolidators, the MOM Administrator Console, and the Web Console server to the database.
The DAS components are based on the Microsoft Universal Data Access platform and use OLE DB application programming interfaces to send data to and receive data from the database. DAS components are installed in Component Services, which provides improved performance using object pooling. The DAS provides centralized database access logic, centralized query logic, shared caching of agent and event information, and pooled connections to the database.
The DAS receives information sent by Consolidators and inserts the information into the database. The DAS also routes processing rules, based on current computer grouping rules, from the database to Consolidators. Consolidators send these processing rules to agents.
The DAS maintains data consistency and logging. For example, when someone changes the resolution state of an alert, the DAS logs all configuration changes, along with the name of the user making the change.
Configuration groups can contain more than one DAS. Having more than one DAS in a configuration group might be necessary for the following reasons:
When a component or interface attempts to send data to or retrieve data from the database, the component or interface requests a DAS from the database computer. The database computer determines the least-loaded DAS and supplies that DAS to the component or interface requesting a DAS. Having more than one DAS in a configuration group spreads the load.
Microsoft Operations Manager 2000 can provide DAS redundancy in a configuration group, which ensures that data is placed in the database even if a DAS is unavailable for some reason.
When you utilize more than one DAS, the database computer determines the least-loaded DAS and supplies that DAS to the component or interface requesting a DAS.
If a Consolidator and a DAS are on the same computer, the Consolidator usually connects to that DAS, while interfaces usually connect to any DAS that Consolidators are not using.
A component or interface will continue to use the same DAS until the DAS service is interrupted for some reason. Consolidators regularly receive updated DAS information from the database, so within 30 minutes, each Consolidator will know if a DAS has failed or if a new DAS has been added to the configuration group. Every DAS can be active at the same time.
The Operations Management Pack module contains several processing rules that generate alerts when a DAS is unavailable, and a redundant DAS takes over.
For more information about multiple Data Access Servers, see the Installation Guide.