The server topology consists of three tiers: front-end Web, application, and database (SQL Server).
All three tiers can be run on a single server.
For larger installations, we recommend that the database tier have a dedicated server (or servers). The front-end Web and application tiers can then be separated according to capacity or administration requirements.
The application server for Microsoft Search Server 2008 can be configured as an index server, a query server, or both. If you configure a particular server for both the index server and query server roles, the content index will not propagate to other query servers.
If the front-end Web and application tiers are being hosted on the same server or servers and are underperforming, we recommend that some or all of the application services be hosted on dedicated servers.
When you move services from front-end Web servers to application servers in order to reduce the load on the Web servers, we recommend that you move the services in the following order: