The only
way to prepare for this type of potentially disastrous situation is to perform regular
backup operations.
Two basic types of potential failures can affect an Oracle database: instance failure,
in which the Oracle instance terminates without going through the shutdown process;
and media failure, in which the disks that store the information in an Oracle
database are corrupted or damaged.
After an instance failure, Oracle will automatically perform crash recovery. For
example, you can use Real Application Clusters to automatically perform instance
recovery when one of its instances crashes. However, DBAs must initiate recovery
from media failure. The ability to recover successfully from this type of failure is the
result of careful planning. The recovery process includes restoring older copies of the
damaged datafile(s) and rolling forward by applying archived and online redo logs.
To ensure successful recovery, the DBA should have prepared for this eventuality by
performing the following actions:
??? Multiplexing online redo logs by having multiple log members per group on different
disks and controllers
??? Running the database in ARCHIVELOG mode so that redo log files are archived
before they are reused
??? Archiving redo logs to multiple locations
??? Maintaining multiple copies of the control file(s)
??? Backing up physical datafiles frequently??”ideally, storing multiple copies in multiple
locations
Running the database in ARCHIVELOG mode ensures that you can recover the
database up to the time of the media failure; in this mode, the DBA can perform
online datafile backups while the database is available for use.
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