SQL Server mirroring protects against data loss in the event of media failure. Mirroring a device continuously duplicates information from one SQL Server device to another. All transactions to the device are copied to its duplicate mirror device. If one of the devices fails, the other contains an up-to-date copy of all transactions. When a read or write to a mirrored device is unsuccessful, it causes the bad device to become unmirrored, and the remaining device takes over.
Note In most cases, the use of hardware-based RAID or Windows NT software-based RAID is recommended over SQL Server mirroring.
For information about setting up SQL Server Mirroring, see Using SQL Server Mirroring, later in this chapter.