Shulou(Shulou.com)06/01 Report--

Let's go back to the files generated during the database backup.

RMAN > backup database Starting backup at 2015-07-08 00:58:27using channel ORA_DISK_1channel ORA_DISK_1: starting full datafile backup setchannel ORA_DISK_1: specifying datafile (s) in backup setinput datafile file number=00001 name=/u01/app/oracle/oradata/devdb/system01.dbfinput datafile file number=00002 name=/u01/app/oracle/oradata/devdb/sysaux01.dbfinput datafile file number=00005 name=/u01/app/oracle/oradata/devdb/example01.dbfinput datafile file number=00003 name=/u01/app/oracle/oradata/devdb/undotbs01.dbfinput datafile file number=00006 name= / u01/app/oracle/oradata/devdb/idx01.dbfinput datafile file number=00004 name=/u01/app/oracle/oradata/devdb/users01.dbfchannel ORA_DISK_1: starting piece 1 at 2015-07-08 00:58:28channel ORA_DISK_1: finished piece 1 at 2015-07-08 01:00:33piece handle=/u01/app/oracle/fast_recovery_area/DEVDB/backupset/2015_07_08/o1_mf_nnndf_TAG20150708T005827_bsr19n9z_.bkp tag=TAG20150708T005827 comment=NONEchannel ORA_DISK_1: backupset complete Elapsed time: 00:02:05channel ORA_DISK_1: starting full datafile backup setchannel ORA_DISK_1: specifying datafile (s) in backup setincluding current control file in backup setincluding current SPFILE in backup setchannel ORA_DISK_1: starting piece 1 at 2015-07-08 01:00:34channel ORA_DISK_1: finished piece 1 at 2015-07-08 01:00:35piece handle=/u01/app/oracle/fast_recovery_area/DEVDB/backupset/2015_07_08/o1_mf_ncsnf_TAG20150708T005827_bsr1flnq_.bkp tag=TAG20150708T005827 comment=NONEchannel ORA_DISK_1: backupset complete Elapsed time: 00:00:01Finished backup at 2015-07-08 01:00:35

A total of two files were generated.

/ u01/app/oracle/fast_recovery_area/DEVDB/backupset/2015_07_08/o1_mf_nnndf_TAG20150708T005827_bsr19n9z_.bkp/u01/app/oracle/fast_recovery_area/DEVDB/backupset/2015_07_08/o1_mf_ncsnf_TAG20150708T005827_bsr1flnq_.bkp

The first file contains backups of six dbf files, and the second file contains backups of control files and spfile. These two files RMAN are called backup sets.

Backup set: a unique format used by RMAN to save backups. A backup set can contain one or more physical files.

There are three backup sets:

Data files: can contain data files and control files, but not archive logs.

Archive logs: contains only archive logs and cannot contain data files or control files.

Backup set: you can back up a backup set in RMAN, that is, a backup set contains a backup set.

Characteristics of backup set

You can use the BACKUP command to create a backup set. The FILESPERSET parameter controls the number of data files included in the backup set.

Backup sets usually contain multiple files.

You can write backup sets to disk or tape.

To extract files from a backup set, you must use a restore operation.

The data file backup set can be an incremental backup or a full backup.

The backup set does not contain blocks that have never been used.

Let's imagine what would be the problem if all the data files generate only one backup set file as the database is backed up as above. When the database is very large, a file generated is also huge. Even if we don't consider whether the operating system has a limit on file size. Such a large file is also very difficult to manage and maintain.

For this reason, Oracle introduced the concept of backup film. If you pay close attention to the backup information above, you will find the words like this.

Piece handle=/u01/app/oracle/fast_recovery_area/DEVDB/backupset/2015_07_08/o1_mf_nnndf_TAG20150708T005827_bsr19n9z_.bkp

The meaning of piece instant backup film. A backup slice physically splits a backup set into one or more files. Let's take a look at the following picture:

Characteristics of backup film

A backup slice is a file in a backup set.

The backup slice can contain blocks of data from multiple data files.

You can use the parameter MAXPIECESIZE to control the maximum size of the backup slice.

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