A media error occurs when a read or write error takes place in a database file due to a physical defect on the disk drive where the file is located. The most frequent physical defect is a head crash, which usually renders all the files on a disk unusable.
In most cases, the database must be recovered after a media error. The recovery strategy depends on the type of damage in the database. You must therefore analyze the error and understand how it was caused before you can continue with the recovery.
Caution
If you are not sure how to perform a recovery, be sure to contact your SAP consultant or an Oracle specialist. Do not attempt a recovery if you are not confident.
An incorrectly performed recovery can lead to irretrievable loss of data in your database. The damage you risk is much more costly than the time you spend on a carefully planned, properly executed recovery of your database.
In addition to the ALERT and trace files, SAP recommends analyzing the database using 
Complete Recovery 
Check the Status of Database Files 
in BRRECOVER. If defects in the data files of the database are involved, BRRECOVER can often perform the database recovery automatically.
See Restore and Recovery with BR*Tools.
This section provides an overview of the recovery process using Oracle SQLPLUS. The sections below contain examples of the command line operations with SQLPLUS.
If you have followed the SAP recommendations regarding the installation and operation of the database system, you should generally succeed in carrying out a complete recovery after a media error. If, however, in an extreme case your backups of the database and your redo log backups have been damaged too, you might only be able to perform an incomplete recovery.
The procedures required for the following errors are listed in the following:
Loss of one or all copies of the control file
Loss of an online or offline redo log file or even an entire online redo log group
Loss of a system, temporary, user, or index tablespace
Error in the archiving process for online redo log files using ARCH
These errors are usually media-related (for example, if the archiving directory for the offline redo log files is lost or full).
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