Backing Up Oracle - Computing at Cornell

Cumulative backups require more storage space than differential backups,
but they are preferable during a restore operation because only one backup
for a given level is needed. See Figure 49.
Note that the first incremental backup must be a level 0 backup that contains
all used blocks. A cumulative backup at level 2 will contain all blocks changed
since the most recent level 1 backup, copying all blocks changed since the
base level 0 backup only if a previous level 1 is unavailable. In contrast to a
cumulative backup, a differential backup at level 2 will determine which level
1 or level 2 backup occurred most recently and copies all blocks changed
since that backup.
Figure 49. Cumulative incremental backups
A cumulative incremental backup is a backup of one or more data files that
contains only those blocks that have changed since a previous backup at a
lower level. A cumulative backup is run by specifying the cumulative option
when defining the backup job.
10.2.4 Image copies
An image copy is a single file (data file, archive log, or control file) that can be
used as-is to perform a recovery. It is similar to an operating system copy of a
single file except that it is produced by an Oracle server process which
performs additional tasks such as validating the blocks in the file and
registering the copy in the control files. An image copy can be done only to
disk.
162 Backing Up Oracle using Tivoli Storage Management