Backup & Recovery Solutions

BACKUP AND RECOVERY SOLUTIONS

What Strategies are available for backing-up of ORACLE DATABASE?

The following methods are valid for backing-up an Oracle database:

• Export/Import - Exports are "logical" database backups in that they extract logical definitions and data from the database to a file. See the Import/ Export FAQ for more details.

• Cold or Off-line Backups - shut the database down and backup up ALL data, log, and control files.

• Hot or On-line Backups - If the database is available and in ARCHIVELOG mode, set the tablespaces into backup mode and backup their files. Also remember to backup the control files and archived redo log files.

• RMAN Backups - while the database is off-line or on-line, use the "rman" utility to backup the database.

What is the difference between Off-line and Online backups?

A hot (or on-line) backup is a backup performed while the database is open and available for use (read and write activity). Except for Oracle exports, one can only do on-line backups when the database is ARCHIVELOG mode.

A cold (or off-line) backup is a backup performed while the database is off-line and unavailable to its users. Cold backups can be taken regardless if the database is in ARCHIVELOG or NOARCHIVELOG mode.

What is the difference between RECOVER and RESTORE database?

RESTORING involves copying backup files from secondary storage (backup media) to disk. This can be done to replace damaged files or to copy/move a database to a new location.
RECOVERY is the process of applying redo logs to the database to roll it forward. One can roll-forward until a specific point-in-time (before the disaster occurred), or roll-forward until the last transaction recorded in the log files

RECOVER DATABASE UNTIL TIME '2001-03-06:16:00:00' USING BACKUP CONTROLFILE;

RMAN> run {

  set until time to_date('04-Aug-2004 00:00:00', 'DD-MON-YYYY HH24:MI:SS');

  restore database;

  recover database;

}

My Database is down and I cannot restore. What now?

Oracle Consulting can sometimes extract data from an offline database using a utility called DUL (Disk UnLoad - Life is DUL without it!). This utility reads data in the data files and unloads it into SQL*Loader or export dump files.

DUDE (Database Unloading by Data Extraction) is another non-Oracle utility that can be used to extract data from a dead database.