Database Mirroring
Another failover option with SQL Server is database mirroring. Database mirroring essentially extends the old log shipping feature of SQL Server and creates an automatic failover capability to a “hot” standby server. Database mirroring is being billed as creating a fault-tolerant database that is an “instant” standby (ready for use in less than three seconds).
At the heart of database mirroring is the “copy-on-write” technology. Copy-on-write means that transactional changes are shipped to another server as the logs are written. All logged changes to the database instance become immediately available for copying to another location. As you can see in Figure 18.9, database mirroring utilizes a witness server as well as client ...
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