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Enhanced features of
RMAN in Oracle 9i
RMAN is an Oracle tool for taking the backup and recovering the
databases. You can copy, restore, and recover datafiles, control files and
archived redo logs. It has command line utility as well as GUI-based
Enterprise Manager Backup. RMAN was initially introduced in Oracle 8 and
lots of new features that made RMAN more powerful were added in Oracle 8i.
With the introduction of Oracle 9i, Oracle improved this tool to have many
more new features that make the database administrators life much easier.
Block Media Recovery
RMAN introduces a new blockrecover command to recover individual
datablocks within a data file. This reduces the Mean Time to Recovery (
MTTR ) for a large datafile when individual blocks within the file are
reported as corrupt. Without this feature, even if a single block is
corrupted the dba has to restore the whole datafile and recovery using the
archived redo logs that were generated since that backup was created.This
procedure is useful when a trace file or standard output reveals that a
small number of blocks within a datafile are corrupt. A major restriction
is that you can only recover from a full RMAN backup and incremental
backups cannot be used for this type of recovery. Also only complete
recovery can be performed on individual blocks and you cannot stop the
redo application while the recovery is in progress.
Block Media recovery can be performed by using a command at the RMAN
command prompt similar to the one given below.
BLOCKRECOVER DATAFILE 6 BLOCK 23 DATAFILE 12 BLOCK 9;
A CONFIGURE command has been introduced in Oracle 9i, that lets you
configure various features including automatic channels, parellelism,
backup options etc., that can persist across sessions and be available to
any session. For example, the CONFIGURE command may be used to store
channel configurations and RMAN will automatically assign the channels as
needed without having to specify the channel allocation as a part of the
script. These automatic allocations and options can be overridden by
commands in an RMAN command file.
Control File Auto Backups
Many of the database administrators stayed away from using RMAN citing
the reliance of RMAN on control files / recovery catalog for backup and
recovery options. Now you need not worry about a lost recovery catalog or
a lost control file. Control File Auto Backups give the dba a way to
restore the backup repository contained in the control file when a control
file and the recovery catalog are both lost. For some of us using the
nocatalog option this comes in very handy when we have to recover without
having the control file that was used for the RMAN backup.
To use this feature, CONFIGURE CONTROLFILE AUTOBACKUP should be set to
ON, and RMAN will automatically perform a control file autobackup after
every BACKUP or COPY command is issued whether its in a RUN Block or at
the command prompt. This control file backup occurs in addition to any
control file backup that has been created as a part of the database
backup.
Other Enhancements
Oracle has enhanced RMAN in oracle 9i with lot many features that make
the job of the dba more error free by enhancing the CHANGE, CROSSCHECK,
DELETE and LIST commands. Also RMAN automatically switches out the online
redo log before backing up the archived redo logs to guarantee that the
backups can be restored to a consistent state. Also the RMAN feature
allows backup only those files that were not backed up after a specified
time. So, if a backup fails partway through, you can restart it and back
up only those files that were not previously backed up.
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