Backing Up Oracle - Computing at Cornell

6.3.3.2 Cumulative incremental backup
A cumulative incremental backup at level n contains only blocks that have
been changed since the most recent backup at level n - 1 or lower.
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 16.
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 16. Cumulative incremental backups
6.3.4 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.
Image copies are not discussed further in this chapter, because RMAN does
not send image copies to TSM — they are always stored locally on disk.
80 Backing Up Oracle using Tivoli Storage Management