Oracle Data Guard can be used to set up one or several slave databases which will be the foundation of a highly available environment. It maintains the standby databases as transaction- consistent copies of the primary database. These instances can be placed in several availability zones.Then, if the production database becomes unavailable because of a planned or an unplanned outage of this instance or of the full availability zone, Data Guard can switch any standby database to the production role, minimizing the downtime associated with the outage. The Active Data Guard module enables read-only access to the standby databases, thereby allowing customers to run read queries and reports on the standby instances, and to perform the backups from a standby instance.
You can have zero data loss by using the appropriate data protection mode:http://docs.oracle.com/cd/B28359_01/server.111/b28294/protection.htm#CHDEDGIF