1. Database Practices
  2. Database Backup Recommendations

7 Database Backup Recommendations

Backup Policy is a very important ingredient of any High Availability system. Oracle recommends RMAN utility for database backup.

RMAN is an acronym for Recovery Manager, which is an Oracle utility that will backup, restore, and recover Oracle data files. RMAN is an Oracle-provided utility for efficiently performing Backup and Recovery. RMAN is available as a part of the standard Installation and, no separate installation is required.

Recovery Manager is a client/server application that uses database server sessions to perform backup and recovery. It stores metadata about its operations in the control file of the target database and, optionally, in a recovery catalog schema in an Oracle database.

You can invoke RMAN as a command-line executable from the operating system prompt or use some RMAN features through the Enterprise Manager GUI.

RMAN Vs Conventional Backup

  • During a conventional hot backup, the amount of Redo generated during the backup would be more due to the fact that the redo logs during the hot backup store the entire block images rather than the change vectors.
  • RMAN doesn’t place the tablespace in a backup mode and hence the amount of Redo generated during the RMAN backup is considerably low.
  • RMAN can identify block corruption during backup operations and RMAN supports Block recovery.
  • RMAN automatically detects new data files and will backup them. Also, RMAN supports the incremental backup method.
  • RMAN backs up only the blocks that have been used at least once. Unused blocks are never backed up. Unused block here refers to the blocks where the block header is zeroed.
  • RMAN enables us to test the backup without actually restoring the backup.
  • RMAN can verify physical and logical structures of the database without actually performing backup.
  • Usage of Shared Pool and Large Pool for RMAN.
  • RMAN uses DBMS_RCVMAN and DBMS_BACKUP_RESTORE packages for backup and recovery. These packages would be loaded in the shared pool for backup and restore operation. RMAN uses the PGA for backup and restore operation.
  • RMAN Requires LARGE_POOL only if TAPE_IO_SLAVES and DBWR_IO_SLAVES are defined.
  • Sizing Large Pool - LARGE_POOL = (Number of Channels) * (16 MB + Tape Buffer)

Benefits of Using RMAN

  • RMAN is an intelligent tool that comes at no extra cost. It is available free with the Oracle Database.
  • RMAN introduced in Oracle 8 and has become simpler with newer versions and easier than user-managed backups.
  • Provides proper security for backups.
  • You can be 100% sure your database has been backed up.
  • The control file and spfile of the database can be configured to be automatically backed up by RMAN.
  • It contains the detail of the backups taken etc. in its central repository Facility for testing the validity of backups also commands like crosscheck to check the status of the backup.
  • Faster backups and restores compared to backups without RMAN.
  • RMAN is the only native backup tool which supports incremental backups.
  • Oracle 19c has got further optimized incremental backup which has resulted in improvement of performance during backup and recovery time.
  • Parallel operations (Multiple Channels for Backup and Restore) are supported.
  • Better querying facility for knowing different details of backup.
  • No extra redo is generated when the backup is performed, compared to conventional online backup.
  • Maintains repository of backup metadata.
  • Remembers backup set location.
  • Knows what needs to back up.
  • Knows what is required for recovery.
  • Knows what backup is redundant.
  • RMAN can back up the Database to Disk or directly to Tape. It is recommended that RMAN backup is performed to disk and then copied to tape.

Backup Strategy Recommendation

RMAN will not backup the below files so it is advised to take the copy of the below files on a regular basis (weekly/any change/addition to the file).

  • Tnsnames.ora
  • Listener.ora
  • Password file
  • Init.ora

The Best practice is to take create the pfile once the spfile is updated.

Below is the recommended strategy.