Oracle Backup Sets
| Backup sets | Contain all the components that make up a full or incremental backup |
| Backup pieces | A single output file containing control and checksum information |
| Full backup sets | A backup of all used blocks |
| Incremental backup sets | A backup of blocks modified since the last backup |
| Multilevel incremental backup sets | A backup where all modified blocks since the last backup of the same or lower level are copied |
| Cumulative incremental backup sets | A backup where all modified blocks since the last lower backup are copied |
| Image copies | An OS-like copy of a single data file |
The basic RMAN commands are RESTORE and RECOVER. RMAN can be used to restore datafiles from backup sets or image copes,
either to their current location or to a new location.
If any archived redo logs are required to complete the recovery operation, RMAN automatically restores and applies them.
In a recovery catalog, RMAN keeps a record containing all the essential information concerning every backup ever taken.
If a recovery catalog is not used, RMAN uses the control file for necessary information.
The RMAN RECOVER command can be used to perform complete media recovery and apply incremental backups, and to perform incomplete media recovery.
Backing Up to a Specific Device Type
Perhaps you have configured different default channels, one to disk and one to tape. You can use the device type parameter to define which automatic channel device you wish to use when the backup begins. Here is an example:
backup database device type disk;
backup database device type sbt;
Controlling Attributes of Backup Sets and Backup Set Pieces
You can control a number of attributes related to backup sets and backup set pieces using options available when you issue the backup command at the RMAN command line.
Here are some of the attributes you can modify (the name of the option is listed in parentheses):
- Backup set size (maxsetsize). Limit the size of any backup set.
- Maximum files per backup set (filesperset). Limit the total number of backup files per backup set.
The default is the number of files to be backed up divided by the number of channels. If the result is less than 64, that becomes the default value for the filesperset parameter.
Otherwise, the default value is 64.
- Include datafiles from at least n disks for each backup set (diskratio).
- Name and location of backup set pieces (format).
- Ignore backup optimization and force a backup of all files specified in the backup set (force).
- Overwrite existing backup set pieces or image copies (reuse).
These options will help you deal with the cases where you need to limit or modify the default behaviors of RMAN. It should be fairly rare to need to use these options, however.
If you find you are using these settings on a regular basis, be sure to review them and determine whether you really need to be using them still.
