With the aid of media recovery, the database administrator can repair a damaged SESAM/SQL database caused by hardware failures where other recovery measures would fail.
Media recovery is based on the following concept:
The database administrator creates SESAM backup copies at carefully selected points in time. He/she can create the backup copies on disk or on magnetic tape cartridge using ARCHIVE or HSMS (utility statement COPY ).
SESAM/SQL does not just allow the whole of the database to be backed up - it also allows smaller units to be backed up. The smallest backup unit supported is a single user space. The time the backup is performed and the choice of appropriate backup units have a considerable effect on the time required by any subsequent recovery measures.
SESAM/SQL logs all changes made to the database after the SESAM backup in log files (CAT logging, DA logging).
The repair of the database or a user space is achieved by resetting to an appropriate SESAM backup copy and then applying the modifications to this copy that have been logged in the log files (CAT-LOG files and DA-LOG files) since.