About RMAN Backups

About Image Copies

An image copy is an exact copy of a single datafile, archived redo log file, or control file. Image copies are not stored in an RMAN-specific format. They are identical to the results of copying a file with operating system commands. RMAN can use image copies during RMAN restore and recover operations, and you can also use image copies with non-RMAN restore and recovery techniques.

To create image copies and have them recorded in the RMAN repository, run the RMAN BACKUP AS COPY command (or, alternatively, configure the default backup type for disk as image copies using CONFIGURE DEVICE TYPE DISK BACKUP TYPE TO COPY before performing a backup). A database server session is used to create the copy, and the server session also performs actions such as validating the blocks in the file and recording the image copy in the RMAN repository.

You can also use an operating system command such as the UNIX dd command to create image copies, though these will not be validated, nor are they recorded in the RMAN repository. You can use the CATALOG command to add image copies created with native operating system tools in the RMAN repository.

About Proxy Copies

During a proxy copy, RMAN turns over control of the data transfer to a media manager that supports this feature. Proxy copy can only be used with media managers that support it, not with disk. The PROXY option of the BACKUP command specifies that a backup should be a proxy copy.

For each file that you attempt to back up with the BACKUP PROXY command, RMAN queries the media manager to determine whether it can perform a proxy copy. If the media manager cannot proxy copy the file, then RMAN backs the file up as if the PROXY option had not been used. (Use the PROXY ONLY option to force RMAN to fail if a proxy copy cannot be performed.)

Proxy copy can be used with datafiles or archived redo logs, as shown in these examples:

BACKUP DEVICE TYPE sbt PROXY DATAFILE 3;
BACKUP DEVICE TYPE sbt PROXY ONLY DATABASE;
BACKUP DEVICE TYPE sbt PROXY ONLY ARCHIVELOG ALL;

The examples assume that sbt channels have been configured with the appropriate parameters.

Note that control files are never backed up with proxy copy. If the PROXY option is specified on an operation backing up a control file, it is silently ignored for the purposes of backing up the control file.

Storage of Backups on Disk and Tape

RMAN can create backups on disk or a third-party media device such as a tape drive. If you specify DEVICE TYPE DISK, then your backups are created on disk, in the file name space of the target instance that is creating the backup. You can make a backup on any device that can store a datafile.

To create backups on non-disk media, such as tape, you must use third-party media management software, and allocate channels with device types, such as SBT, that are supported by that software.

Backups of Archived Logs

There are several features of RMAN backups specific to backups of archived redo logs.

BACKUP ARCHIVELOG FROM SEQUENCE 121 UNTIL SEQUENCE 125;

Multiplexed Backup Sets

When creating backup sets, you can multiplex files. In this case, RMAN simultaneously reads multiple files from disk and and then writes their blocks into the same backup set. (Image copies, by contrast, are never multiplexed.) For example, RMAN can read from two datafiles simultaneously, and then combine the blocks from these datafiles into a single backup piece.

As Figure 2-2 illustrates, RMAN can back up three datafiles into a backup set that contains only one backup piece. This backup piece contains the intermingled data blocks of the three input files.

Figure 2-2 Datafile Multiplexing

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Multiplexing by the Media Manager

Media manager multiplexing occurs when the media manager writes the concurrent output from multiple RMAN channels to a single sequential device, such as a tape drive.

Manual Parallelization of Backups

When you configure PARALLELISM to greater than 1 or manually allocate multiple channels, RMAN writes multiple backups sets or image copies in parallel. The channels divide the work of backing up the specified files.

By default, RMAN determines which channels should back up which database files. You can use the CHANNEL option of the BACKUP command to manually assign a channel to back up specified files. This example shows a parallelized backup to the default disk location that uses the default automatic DISK channels:

BACKUP
  (DATAFILE 1,2,3 
   CHANNEL ORA_DISK_1)
  (DATAFILECOPY '/tmp/system01.dbf', '/tmp/tools01.dbf'
   CHANNEL ORA_DISK_2)
  (ARCHIVELOG FROM SEQUENCE 100 UNTIL SEQUENCE 102 THREAD 1 
   CHANNEL ORA_DISK_3);

You can also manually allocate channels as in the following example:

RUN 
{
  ALLOCATE CHANNEL c1 DEVICE TYPE sbt PARMS="ENV=(BACKUP_SERVER=tape_server1)";
  ALLOCATE CHANNEL c2 DEVICE TYPE sbt PARMS="ENV=(BACKUP_SERVER=tape_server2)";
  ALLOCATE CHANNEL c3 DEVICE TYPE sbt PARMS="ENV=(BACKUP_SERVER=tape_server3)";
  BACKUP
   (DATAFILE 1,2,3
    CHANNEL c1)
   (DATAFILECOPY '/tmp/system01.dbf', '/tmp/tools01.dbf'
     CHANNEL c2)
   (ARCHIVELOG FROM SEQUENCE 100 UNTIL SEQUENCE 102 THREAD 1
     CHANNEL c3);
}

Figure 2-3 shows an example of parallelization in which channel ch1 backs up datafiles, channel ch2 backs up datafile copies, and channel ch3 backs up logs.

Figure 2-3 Parallelization of Backups

Description of the illustration bradv024.gif