Media Recovery

Datafile media recovery is sometimes alse called media recovery.

Datafile media recovery is used to recover from a damaged (or lost) datafile, control file or spfile. The goal of datafile media recovery is to restore database integrity.

In order for a datafile to be able to be recovered, either:

• The database is not open, or
• The datafile is offline

A datafile that needs media recovery cannot be brought online. A database cannot be opened if any of the online datafiles need media recovery.

A media recovery sort of replays the redo generated to a restored block to make that block as of a certain time. Recovery of a datafile always begins with the lowest SCN recorded in the datafile header.

Datafile media recovery differs from crash recovery in the following points:

• Oracle will not initiate media recovery on its own, it must be explicetly demanded by a DBA.
• It will restore a datafile saved away in a backup. Crash recovery recovers a datafile that was left by a crash.
• Media recovery uses uses both archived redo logs and online redo log to recover. Crash recovery only needs the redo logs.

• A datafile off a backup is restored
• A backed up control file is restored
• A datafile is taken offline without the offline normal option.