S 6.51 Restoring a database

Initiation responsibility: Head of IT Section, IT Security Management

Implementation responsibility: Administrators

It is necessary to prepare a concept describing how database backups are to be restored. This concept must be structured in accordance with

• The data backup policy (refer to S 6.49 Data backup in a database) and

• Potential error situations creating a need for the restoration of data backups.

These two aspects should be used as a basis for determining which database backups are to be restored using which techniques.

The restoration of a database is a complex task which must be performed carefully by experienced personnel. In spite of this, errors and hitches must always be reckoned with during a restoration. For this reason, a damaged database should not be overwritten simply by restoring the database backup.

In many cases, a seemingly corrupt database can be fixed again. In order to minimise the restart time however, trouble shooting should be accompanied by an attempt to restore the database in a separate storage area. Even if damaged data can no longer be repaired, it should be retained so that it can be analysed and the cause of the error can be determined.

During restoration, the database backup should therefore first be loaded on a separate storage medium. Here, it must be noted that the backup requires the same amount of disk space as the defective database.

This disk space must be reserved for emergencies, in order to prevent a loss of database integrity and meet availability requirements. If this is not possible, it is necessary to determine a technique whereby the required disk space can be made available at short notice. Naturally, this should not result in an additional loss of data, for example if areas of the hard disk holding other data need to be overwritten in order to release the resources necessary for loading the database backup. If data nevertheless needs to be deleted due to a lack of disk space, it must first be backed up carefully to ensure that it can be made fully available again after restoration has been completed.

If only individual data records need to be restored instead of the entire database, the backup data should always be loaded separately from the original data. Corresponding disk space must be available in this case, too. Here, it is more advisable to configure a separate database so as to ensure that the original database remains unaffected at all events. This applies even if it is possible to read the backup data individually into the original database.

Additional controls:

• Has a concept for the restoring of database backups been prepared?

• When was the restoring of database backups last rehearsed?

• Has enough disk space been reserved for emergencies?