Free/busy data is information about the availability of individuals within an organization at specified times. The user status data indicates whether the time period specified is free, busy or tentative, or if the user has set their out of office status. However, the data contains no explanatory information, such as whether the user is in a meeting or has a personal appointment or whether they are physically in the office at the requested time.
Free/busy data allows people to find available slots for appointments and meetings in other users' calendars, even if they cannot confer with the user. Exchange Server and Outlook Web App (OWA) both use free/busy data to track user availability.
The data in a user's free/busy file contains only about 100 bytes, so storing, managing, and replicating it places minimal demand on network resources. However, free/busy data replication affects how up-to-date the data is. If only one copy of free/busy information exists per user, then OWA must connect to that specific file. If the server is distant and network traffic is heavy, response time might be unacceptably slow. In that case, free/busy data can be replicated on multiple servers, but because of lag times inherent in replication, some copies of the data are likely to be obsolete at any given time.
Because of the complexity involved, OWA does not merge new data into existing data. Instead, it deletes a user's existing free/busy data and writes new data that represents the current calendar state.