Simple Recovery ModelThe simple recovery model is just that: simple. In this approach, SQL Server maintains only a minimal amount of information in the transaction log. SQL Server truncates the transaction log each time the database reaches a transaction checkpoint, leaving no log entries for disaster recovery purposes.
In databases using the simple recovery model, you may restore full or differential backups only. It is not possible to restore such a database to a given point in time, you may only restore it to the exact time when a full or differential backup occurred. Therefore, you will automatically lose any data modifications made between the time of the most recent full/differential backup and the time of the failure.
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Full Recovery ModelThe full recovery model also bears a self-descriptive name. With this model, SQL Server preserves the transaction log until you back it up. This allows you to design a disaster recovery plan that includes a combination of full and differential database backups in conjunction with transaction log backups.
In the event of a database failure, you have the most flexibility restoring databases using the full recovery model. In addition to preserving data modifications stored in the transaction log, the full recovery model allows you to restore a database to a specific point in time. For example, if an erroneous modification corrupted your data at 2:36AM on Monday, you could use SQL Server’s point-in-time restore to roll your database back to 2:35AM, wiping out the effects of the error.
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Bulk-logged Recovery ModelThe bulk-logged recovery model is a special-purpose model that works in a similar manner to the full recovery model. The only difference is in the way it handles bulk data modification operations. The bulk-logged model records these operations in the transaction log using a technical known as minimal logging. This saves significantly on processing time, but prevents you from using the point-in-time restore option.
Microsoft recommends that the bulk-logged recovery model only be used for short periods of time. Best practice dictates that you switch a database to the bulk-logged recovery model immediately before conducting bulk operations and restore it to the full recovery model when those operations complete.
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Those are the basics of SQL Server recovery models. For more information on designing a disaster recovery plan using these models, read SQL Server Backup.