Differential Backup and Restore

A differential backup makes a copy of all the pages in a database that have been modified after the last database backup. Differential logs are used primarily in heavily used systems where a failed database must be brought back online as quickly as possible. Differential backups are smaller than full database backups, so they make less of an effect on the system while they run.

Assume a site does a full database backup on Sunday night. They make a set of transaction log backups every 4 hours during the day, with the backups from one day overwriting the backups from the day before. Each night they make a differential backup. If one of the data disks for the database fails at 9:12 A.M. on Thursday, the site can:

  1. Back up the current transaction log.
  2. Restore the database backup from Sunday night.
  3. Restore the differential backup from Wednesday night to roll the database forward to that point.
  4. Restore the transaction log backups from 4 and 8 A.M. to roll the database forward to 8 A.M.
  5. Restore the log backup taken after the failure. This will roll the database forward to the time of the failure.
See Also

Differential Database Backups

  


(c) 1988-98 Microsoft Corporation. All Rights Reserved.