[From SQL Server Central
Database Mirroring is a major new technology for achieving high availability in SQL Server 2005. Database Mirroring operates at a database level and is configured on a database-by-database basis. The primary goal of database mirroring is to increase data availability and allow failover in case a server hosting the database becomes unavailable. So including Database Mirroring now we have 4 High Availability in SQL Server 2005 (1) Clustering (2) Log Shipping (3) Replication (Transactional) (4)Mirroring. I can say that Database Mirroring is Log Shipping with automatic failover per database & Clustering on database level without single point of failure without shared disk.
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