Mirroring the Team Foundation Data-Tier Server
You can synchronize your data-tier server for Team Foundation with a copy on another server in a process that is referred to as database mirroring. The server that hosts the original database becomes the principal server, and the server that hosts the copy becomes the mirroring server. By mirroring your data-tier server, you can manually switch over from the principal server to the mirroring server if the hardware fails or you must perform maintenance.
Mirroring the data-tier server complements other availability and recovery strategies for Team Foundation, such as setting up a standby application-tier server, and supplements backup and restore strategies. However, you should not consider mirroring a replacement strategy for regular backups. For more information, see Ensuring Team Foundation Server Availability and Managing Team Foundation Server Backups.
If you configure database mirroring, the databases on the principal server are synchronized with copies on the mirroring server. However, Team Foundation Server can use only the principal server's databases unless you manually fail over to the mirroring server. Communication between the principal and mirroring servers can be either asynchronous or synchronous.
If you fail over the servers, the mirror server takes over the principal role and brings its copy of the database online as the new principal database. The former principal server, if available, assumes the mirror role, and its database becomes the new mirror database. Potentially, the roles can switch back and forth repeatedly. For more information about failover, see the following topics on the Microsoft Web site: