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Backup - Multisection for Very Large Files

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• Backup - Multisection for Very Large Files
  • Multisection Large File Backup
  • Views
  • Command

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Multisection Large File Backup

• Multisection backups of a single file:
  • Are created by RMAN, with your specified size value
  • Are processed independently (serially or in parallel)
  • Produce multipiece backup sets and image copies
  • Improve performance of the backup

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• Oracle data files can be up to 128 TB in size.

  • Normally, the smallest unit of an RMAN backup is an entire file.

• Multisection

  • break up large files into sections and back up and restore these sections independently.
  • can be done for backup sets and image copies.
  • can improve the performance of the backup operation
  • allows large file backups to be restarted.

• Each file section:

  • a contiguous range of blocks of a file.
  • can be processed independently,
    • either serially
    • or in parallel.

• A multisection backup job produces a multipiece backup set.

  • Each piece contains one section of the file.
  • All sections of a multisection backup, except perhaps for the last section, are of the same size.
  • a maximum of 256 sections per file.

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• Multisection backups of a single data file are:
  • Created by RMAN, with your specified size value
  • For backup sets and image copies
  • For full and incremental backups
• Benefits:
  • Reduce image copy creation time
  • Are processed independently (serially or in parallel)
  • Benefit Exadata
  • Do not apply large values of parallelism to back up a large file that resides on a small number of disks.

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• Multisection image copies

  • reduce the image copy creation time for large data files, in particular benefiting Exadata environments.
  • reduce completion time for nonbackup use cases
    • e,g,.copying a file as part of transportable tablespace procedure or creating a clone with active database duplication.

• should not apply large values of parallelism to back up a large file that resides on a small number of disks,

  • because that would defeat the purpose of the parallel operation.
  • Multiple simultaneous accesses to the same disk device would be competing with each other.

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Views

View	Description
V$BACKUP_SET	displays information about backup sets from the control file.
V$BACKUP_DATAFILE	displays information about control files and data files in backup sets from the control file.
RC_BACKUP_SET	lists information about backup sets for all incarnations of the database.
RC_BACKUP_DATAFILE	lists information about data files in backup sets.

• the MULTI_SECTION column in RC_BACKUP_SET and V$BACKUP_SET

  • indicates whether this is a multisection backup or not.

• the SECTION_SIZE column in V$BACKUP_DATAFILE and RC_BACKUP_DATAFILE

  • specifies the number of blocks in each section of a multisection backup.
  • Zero means a whole-file backup.

SELECT MULTI_SECTION FROM V$BACKUP_SET;

SELECT SECTION_SIZE FROM V$BACKUP_DATAFILE;

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Command

-- Backup datafile with a specific secion size
BACKUP <options> SECTION SIZE <integer> [K | M | G]
-- Validate datafile with a specific secion size
VALIDATE DATAFILE <options> SECTION SIZE <integer> [K | M | G]

-- e.g.,
BACKUP DATAFILE 5 SECTION SIZE = 25M TAG 'section25mb';

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