RMAN FULL BACKUP VS. LEVEL 1 INCREMENTAL
By default, RMAN makes full backups. A full backup of a data file includes
every allocated block in the file being backed up. A full backup of a data file
can be an image copy, in which case every data block is backed up. It can also
be stored in a backup set, in which case data file blocks not in use may be
skipped.
A full backup is the default type of RMAN backup. A full backup
has no effect on subsequent incremental backups and is not considered a part of
an incremental backup strategy.
Image copies are always full backups because they include every data block in a
data file. A backup set is by default a full backup because it can potentially
include every data block in a data file, although unused block compression means that blocks never used are
excluded and, in some cases, currently unused blocks are excluded.
In contrast to a full backup, an incremental backup copies only
those data blocks that have changed since a previous backup. You can use RMAN
to create incremental backups of data files, tablespaces, or the whole
database. A full backup cannot be part of an incremental backup strategy; that
is, it cannot be the parent for a subsequent incremental backup.
Multilevel
Incremental Backups
RMAN can create multilevel incremental backups. Each incremental
level is denoted by a value of 0 or 1. A level
0 incremental backup, which is the base for subsequent incremental backups, copies
all blocks containing data.
The only difference between a level 0 incremental backup and a
full backup is that a full backup is never included in an incremental strategy.
Thus, an incremental level 0 backup is a full backup that happens to be the
parent of incremental backups whose level is greater than 0.
A level 1 incremental backup can be either of the following
types:
·
A differential incremental backup, which
backs up all blocks changed after the most recent incremental backup at level 1
or 0
·
A cumulative incremental backup, which
backs up all blocks changed after the most recent incremental backup at level 0 Incremental backups are differential by default.
Incremental backups at level 0 can be either backup sets or
image copies, but incremental backups at level 1 can only be backup sets.
Differential
Incremental Backups
In a differential level 1 backup, RMAN backs up all blocks
that have changed since the most recent incremental backup at level 1
(cumulative or differential) or level 0.
For example, in a differential level 1 backup, RMAN determines
which level 1 backup occurred most recently and backs up all blocks modified
after that backup. If no level 1 is available, then RMAN copies all blocks
changed since the base level 0 backup.
If no level 0 backup is available in either the current or
parent incarnation, then
the behavior varies with the compatibility mode setting. If compatibility is
>=10.0.0, RMAN copies all blocks that have been changed since the file was
created. Otherwise, RMAN generates a level 0 backup.
·
Sunday
An incremental level 0 backup backs up all blocks that have ever been in use in this database.
·
Monday through Saturday
On each day from Monday through Saturday, a differential incremental
level 1 backup backs up all blocks that have changed since the most recent
incremental backup at level 1 or 0. The Monday backup copies blocks changed
since Sunday level 0 backup, the Tuesday backup copies blocks changed since the
Monday level 1 backup, and so forth.
Cumulative
Incremental Backups
In a cumulative level 1 backup, RMAN backs up all blocks
used since the most recent level 0 incremental backup in either the current or
parent incarnation. Cumulative incremental backups reduce the work needed for a
restore operation by ensuring that you only need one incremental backup from
any particular level.
Cumulative backups require more space and time than differential
backups because they duplicate the work done by previous backups at the same
level.
·
Sunday
An incremental level 0 backup backs up all blocks that have ever been in use in this database.
·
Monday - Saturday
A cumulative incremental level 1 backup copies all blocks
changed since the most recent level 0 backup. Because the most recent level 0
backup was created on Sunday, the level 1 backup on each day Monday through
Saturday backs up all blocks changed since the Sunday backup.
Block
Change Tracking
The block change tracking feature
for incremental backups improves incremental backup performance by recording
changed blocks in each data file in a block change tracking file. This file is a small binary
file stored in the database area. RMAN
tracks changed blocks as redo is generated.
If block change tracking is enabled, then RMAN uses the change
tracking file to identify changed blocks for incremental backups, thus avoiding
the need to scan every block in the data file. RMAN only uses block change
tracking when the incremental level is greater than 0, because a level 0 incremental backup includes
all blocks.
Ref: www.docs.oracle.com
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