Database Reference
In-Depth Information
Memory buffers
(PGA or SGA):
RMAN uses a memory area in the PGA (and sometimes in
the SGA) as a buffer when reading from data files and copying subsequent blocks to back
up files.
Auxiliary database:
A database to which RMAN restores target database data files for the
purpose of duplicating a database, creating a Data Guard standby database, or performing
a DBPITR.
Backup/Back up:
Can be either a noun or a verb. The physical files (backup) that store the
backed up files; or, the act of copying and archiving (backing up) files. Backups can consist
of backup sets and backup pieces or image copies.
Backup set:
When you run an RMAN
BACKUP
command, by default, it creates one or more
backup sets. A backup set is a logical RMAN construct that groups backup piece files. You
can think of the relationship of a backup set to a backup piece as similar to the relationship
between a tablespace and a data file: one is a logical construct, the other is a physical file.
Backup piece file:
RMAN binary backup files. Each logical backup set consists of one or
more backup piece files. These are the physical files that RMAN creates on disk or tape.
They're binary, proprietary format files that only RMAN can read or write to. A backup
piece can contain blocks from many different data files. Backup piece files are typically
smaller than data files, because backup pieces only contain blocks that have been used in
the data files.
Image copy:
Initiated with the
BACKUP AS COPY
command. A type of backup in which
RMAN creates identical copies of a data file, archive redo log file, or control file. Image
copies can be operated on by OS utilities such as the Linux
cp
and
mv
commands. Image
copies are used as part of incrementally updated image backups. Sometimes, it's preferable
to use image copies rather than backup sets if you need to be able to restore quickly.
Recovery catalog:
An optional database schema that contains tables used to store
metadata information regarding RMAN backup operations. Oracle strongly recommends
using a recovery catalog, because it provides more options for B&R.
Media manager:
Third-party software that allows RMAN to back up files directly to tape.
Backing up to tape is desirable when you don't have enough room to back up directly to
disk or when disaster recovery requirements necessitate a backup to storage that can be
easily moved offsite.
FRA:
An optional disk area that RMAN can use for backups. You can also use the FRA to
multiplex control files and online redo logs. You instantiate a fast recovery with the database
initialization parameters
DB_RECOVERY_FILE_DEST_SIZE
and
DB_RECOVERY_FILE_DEST
.
Snapshot control file:
RMAN requires a read-consistent view of the control file when either
backing up the control file or synchronizing with the recovery catalog (if it's being used).
In these situations, RMAN first creates a temporary copy (snapshot) of the control file. This
allows RMAN to use a version of the control file that is guaranteed not to change while
backing up the control file or synchronizing with the recovery catalog.
You can make several types of backups with RMAN:
Full backup:
All modified blocks associated with the data file are backed up. A full backup is
not a backup of the entire database. For example, you can make a full backup of one data file.
Incremental level 0 backup:
Backs up the same blocks as a full backup. The only difference
between a level 0 backup and a full backup is that you can use a level 0 backup with other
incremental backups, but not a full backup.
