Using RMAN compression for backups

As the databases keep growing, so does the space occupied by their backups. Fortunately, RMAN has built-in support to compress such large sized backups which can be handy rather than using an OS utility such as TAR or so on. The following are the two kinds of compression techniques used by RMAN:

• Block Compression

• Binary Compression

RMAN uses block compression by default and that's why you can't set it off (or on either). Two modes of block compression are available, Unused Block Compression (UBC) and Null Block Compression (NBC). In NBC, all the empty blocks which were not used are skipped. This mode is always used in level 0 and for full backups. In UBC, blocks which are not used by any object are not read or included in the backups. Even the blocks which were used in the past but are empty now (for example, blocks after a truncate table or drop table operation) are skipped. Unlike NBC, which works for all the backups, UBC only works for disk-based backups...