Differential Backup and Restore
A differential backup creates a copy of all the pages in a database modified after the last database backup. Differential logs are used primarily in heavily used systems where a failed database must be brought back online quickly. Differential backups are smaller than full database backups; therefore, they have less of an effect on the system while they run.
For example, a site executes a full database backup on Sunday night. A set of transaction log backups is made every four hours during the day, with the backups from one day overwriting the backups from the day before. Each night the site makes a differential backup. If one of the data disks for the database fails at 9:12 A.M. on Thursday, the site can:
- Back up the current transaction log.
- Restore the database backup from Sunday night.
- Restore the differential backup from Wednesday night to roll the database forward to that point.
- Restore the transaction log backups from 4:00 A.M. and 8:00 A.M. to roll the database forward to 8:00 A.M.
- Restore the log backup taken after the failure. This will roll the database forward to the time of the failure.