Determining Which Devices to Mirror

When deciding to mirror a device, you must weigh such factors as the costs of system downtime, possible reduction in performance, and the cost of storage media. Considering these issues can help you decide whether to mirror only the transaction logs, all devices on a server, or selected devices.

Note: You cannot mirror a dump device.

Mirror all default database devices so that you are protected if a create or alter database command affects a database device in the default list.

In addition to mirroring user database devices, put transaction logs on a separate database device. For even greater protection, mirror the database device used for transaction logs.

To put a database’s transaction log (that is, the system table syslogs) on a different device than the one on which the rest of the database is stored, name the database device and the log device when you create the database. You can also use alter database to add a second device and then run sp_logdevice.

When weighing cost and performance trade-offs, consider: