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Image Copies and Backup Sets

Databasc backups created by RMAN arc storcd as image copies or backup sets.

Image copies arc exact bytc-for-byte copies of files. You can create an image copy by copying a file at the operating system level. Unlikc copying files at the operating system level, however, image copies created through RMAN arc recorded in the RMAN repository so that RMAN can use these copies during databasc restore operations and recovcry. RMAN can restore files only if they are recorded in the RMAN repository. RMAN can create image copies only on disk.

Backup sets are logical entities produced by the RMAN BACKUP command. This command can producc one or morę backup sets on disk or tape deviccs. Although image copies cannot use all RMAN features. their advantages arc that you can apply incremcntal backups to them (synthetie fuli backups) and you can use them dircctly in place without first copying them, for vcry fast restores.

Each backup set contains one or morę physical files callcd backup pieces. A backup piece Stores the backup of one or morę databasc files in a compact RMAN-spccific format. One advantage of backup sets is that RMAN uses unused błock compression to save space in backing up data files. Only those blocks in the data files that have been used to storę data are included in the backup set. Backup sets can also be compressed, enerypted, sent to tape, and use advanced unused-space compression that is not availabie with datafile copies.