Databases Reference
In-Depth Information
• Automatically parallelizes both the reading and writing of the various Oracle files
being backed up
RMAN performs the full backup operations and updates a catalog (stored in an Oracle
Database) with the details of what backups were taken and where they were stored. You
can query this catalog for critical information, such as datafiles that have not been backed
up or datafiles whose backups have been invalidated through NOLOGGING operations
performed on objects contained in those datafiles.
RMAN also uses the catalog to perform incremental backups. RMAN will back up only
database blocks that have changed since the last backup. When RMAN backs up only
the individual changed blocks in the database, the overall backup and recovery time can
be significantly reduced for Oracle databases in which a small percentage of the data in
large tables changes. Improvements in methods used by RMAN in recent Oracle releases
have greatly enhanced performance for incremental backups.
RMAN reads and writes Oracle blocks, not operating system blocks. While RMAN is
backing up a datafile, Oracle blocks can be written to it, but RMAN will read and write
in consistent Oracle blocks, not operating system blocks within an Oracle block.
The following list summarizes the RMAN capabilities that enable high availability:
• Automated channel failover during backup and restore
• Automated failover to a previous backup during restore when the current backup
is missing or corrupt
• Automated new database and temporary file creation during recovery
• Automated recovery to a previous point in time
• Block media recovery while the datafile is online
• Block change tracking for fast incremental backups
• Merged incremental backups
• Backup and restore of required files only
• Retention policy ensuring that relevant backups are available
• Resumable backup and restore if operations failed
• Automatic backup of the control file and server parameter file
Since Oracle Database 10
g
, RMAN is also used to support automated disk-based backup.
Disk-based strategies have an advantage over tape: they enable random access to any
data such that only changes need be backed up or recovered. RMAN can be set up to
run a backup job to disk at a specific time. RMAN manages the deletion of backup files
that are no longer necessary. In combination with ASM, RMAN will write all backups,
