Backup commnd formats can be checked at this link >> backup-command
Files That RMAN Can Back Up :
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1) Database files, including datafiles, control files, and the server parameter file (SPFILE)
2) Archived redo logs
3) Other backups created by RMAN, including such as datafile and control file image copies, and backup sets containing SPFILEs, control files,
datafiles and archived logs
RMAN Backup Formats
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1) Image Copies
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> A bit-for-bit duplicate of a database file, identical to a copy made with an operating system command.
> RMAN can create image copies of datafiles and datafile copies, control files and control file copies, archived redo logs, and backup pieces.
2) Backup Sets
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> Storing backup information a logical structure called backup set.
> Contains the data from one or more datafiles, archived redo logs, or control files or SPFILE. (Datafiles and archivelogs cannot be mixed together
in the same backup set.)
> Can also back up existing backup sets into another backup set.
> Backup set consists of one or more files in an RMAN-specific format, known as backup pieces.
> Only RMAN can create or restore from backup sets
> Default backup type
> When backing up datafiles to backup sets, RMAN is able to skip some datafile blocks that do not currently contain data, reducing the size of backup sets and the time required to create them. This behavior, known as unused block compression . This behavior is fundamental to how RMAN writes
datafiles into backup pieces, and cannot be disabled.
> RMAN also supports binary compression of backup sets
RMAN Backup Types
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1) Full datafile backups
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> A full backup of a datafile is a backup that includes every used data block in the file.
2) Incremental backups
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> An incremental backup of a datafile captures images of blocks in the datafile changed since a specific point in time, usually the time of a
previous incremental backup.
> Incremental backups are always stored as backup sets.
> The resulting backup sets are generally smaller than full datafile backups, unless every block in the datafile is changed ( very unlikely ).
> RMAN can only create incremental backups of datafiles, not of archived redo log files or other files.
> Recovery using incremental backups is much faster than applying changes one at a time from the archived redo logs as RMAN uses the block
images from incremental backups, to update changed blocks to their contents at the SCN where the block was created in a single step.
Specifying Tags for RMAN BACKUP
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> RMAN attaches an identifier called a tag to every backup it creates, as a way of identifying that backup that can be used with later RMAN commands.
> ASM does not support the use of the - character in the filenames it uses interally, so a tag including a - (such as weekly-incremental) is not a legal tag name
Using Compressed Backupsets for RMAN Backup
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> RMAN can do binary compression by using the AS COMPRESSED BACKUPSET option to the BACKUP command.
> No extra uncompression steps are required during recovery if you use RMAN's integrated compression.
> The primary disadvantage of using RMAN binary compression is performance overhead during backups and restores
Consistent and Inconsistent Backups with RMAN
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1) Consistent Backups
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> Taken when the database is in a consistent state, that is, one taken after the database has been shut down normally (using SHUTDOWN NORMAL, SHUTDOWN IMMEDIATE or SHUTDOWN TRANSACTIONAL).At this point, all changes in the redo log have been applied to the datafiles. If you mount the database and take a backup at this point, then you can restore the database from this backup at a later date and open it without performing
media recovery.
>
2) Inconsistent Backups
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> Any backup taken when the database has not been shut down normally is an inconsistent backup. When a database is restored from an inconsistent backup, Oracle must perform media recovery before the database can be opened, applying any pending changes from the redo logs.
Difference between RMAN and user-managed online backups
When performing user-managed backups, taking online backups required that you place your datafiles into backup mode using the ALTER DATABASE/TABLESPACE BEGIN BACKUP statement. RMAN does not require the use of backup mode for the creation of online backups. Do not use ALTER DATABASE/TABLESPACE BEGIN BACKUP before an RMAN backup.