SQL 05 Database Mirroring is a cool technology
SQL Server's current 3 High Availability features - Clusering, Replication & Log Shipping are all good for different purposes but each has it's own draw-backs & none are good for all scenarios. Eg, clustering can be expensive to implement & you don't get geographically dispersed disk level fault tolerance. Some services (eg Analysis Services) won't even run on clustered servers. Replication has some advantages but is complicated & has far too many moving parts to be considered simple or self managing. And Log Shipping requires a little too much manual intervention for many non-specialist SQL Server IT Pros.
SQL Server 2005's Database Mirroring technology looks like a great middle ground technology, with the best of Clustering & Log Shipping built in. It's conceptually similar to Log Shipping in that transactions are "synchronised" from a primary server to a stand-by server (similar to Log Shipping) but health is monitored by a "Witness" server and automatic fail-over can be configured (like Clustering). Database Mirroring doesn't require certified hardware & can work over geographically dispersed locations like Log Shipping.
Secure Data Group's Craig Ryan provided an exceptional presentation at the Melbourne User Group meeting last week, including a live presentation of all three current High Availability technologies & SQL 05's Database Mirroring. I was really impressed with the ease of setup & also Craig's advanced planning - sure enough, whenever you present Beta software, it's gonna let you down but Craig was prepared with a backup plan which he promptly put into action to the relief of everyone there. Great job Craig!