Restoring files from a differential backup is a process somewhat similar to restoring from an incremental backup, except the number of tapes required differs. When you’re restoring all files from a differential backup, the process is as follows:

  1. Restore the files from the last full backup.
  2. Restore the files from the last differential backup.

As this process shows, the differential restore requires only two backup sets to be restored.

Note: A backup set is the collection of files that were backed up during one backup session. A backup set can span multiple backup media types.

For example, a company performs a full backup every Sunday evening and differential backups every Monday through Saturday evening. If the system fails on Friday morning, after the system is repaired, only two backup sets are required to put the system and all the data back in the state they were in before the crash. The two backup sets would be from Sunday night (to restore all files) and Thursday night (to update all the changed files since Sunday).

The differential restore requires less time, but the differential backup requires more time as the week progresses. Therefore, if your company does not care about the time it takes to backup a server but wants the server to be restored as quickly as possible, the differential backup type is the best solution.

Every so often, data that is backed up should be temporarily restored to an alternate location to determine whether the backup is being performed without error.

Sometimes companies back up their file servers on a regular basis only to learn at a later date when a file needs to be restored that no backups have been occurring. The backup media tapes are all blank. There were no errors in any of the backup logs, and all seemed normal; however, the backup hardware had failed and no errors were generated.

[tags]diana huggins,data protection,disaster planning & recovery,data loss,backup plan[/tags]