Image Copies and Backup Sets
Database backups created by RMAN are stored as image copies or backup sets.
Image copies are exact byte-for-byte copies of files. You can create an image copy by
copying a file at the operating system level. Unlike copying files at the operating
system level, however, image copies created through RMAN are recorded in the
RMAN repository so that RMAN can use these copies during database restore
operations and recovery. 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 produce one or more backup sets on disk or tape devices. Although
image copies cannot use all RMAN features, their advantages are that you can apply
incremental backups to them (synthetic full backups) and you can use them directly in
place without first copying them, for very fast restores.
Each backup set contains one or more physical files called backup pieces. A backup
piece stores the backup of one or more database files in a compact RMAN-specific
format. One advantage of backup sets is that RMAN uses unused block compression
to save space in backing up data files. Only those blocks in the data files that have
been used to store data are included in the backup set. Backup sets can also be
compressed, encrypted, sent to tape, and use advanced unused-space compression
that is not available with datafile copies.
... zobacz całą notatkę