What is DUPLEX in RMAN

 

In RMAN, the SET DUPLEX command is used to create multiple copies of the same backup, a process known as backup duplexing. 

This feature ensures that multiple identical copies of a backup are generated simultaneously, which enhances redundancy and safeguards against backup corruption or media failures.

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What is DUPLEX in RMAN?

• DUPLEX specifies how many copies of a backup RMAN should create in a single operation.

• The backup copies are identical and are written to the specified locations or devices.

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Syntax Example:

SET DUPLEX = 2;
BACKUP DATABASE;

• This creates 2 copies of each backup piece during the backup operation.

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How it Works

• When you allocate channels (e.g., ch1 in your example), RMAN writes the specified number of copies of each backup piece to the designated destination(s).

• If you specify DUPLEX=2, RMAN writes two identical backup sets to the configured destinations.

• Duplexing works with both disk and SBT_TAPE backups.

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Practical Example:-

Tape Backup with Duplexing:

RMAN> ALLOCATE CHANNEL ch1 DEVICE TYPE SBT_TAPE PARMS 'ENV=(TDPO_PROFILE=/usr/tivoli/tsm/client/oracle/bin64/tdpo.opt)';

RMAN> SET DUPLEX = 2;

RMAN> BACKUP DATABASE PLUS ARCHIVELOG;

• This command backs up the database to the tape device and creates two identical copies of each backup piece.

Disk Backup with Duplexing:

RMAN> CONFIGURE DEVICE TYPE DISK PARALLELISM 1 BACKUP TYPE TO BACKUPSET;

RMAN> SET DUPLEX = 2;

RMAN> BACKUP DATABASE FORMAT '/backup/dir1/db_%U', '/backup/dir2/db_%U';

• Here, the backup pieces are duplicated and stored in two separate directories (/backup/dir1 and /backup/dir2).

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Advantages of DUPLEX

• Increased Redundancy: Multiple backup copies provide additional safety in case of media failure or corruption.

• Streamlined Operations: Both copies are created simultaneously, saving time compared to running the backup twice.

• Compliance: Useful for meeting regulatory or organizational requirements for multiple backup copies.

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Limitations of DUPLEX

• Resource Usage: Requires more storage space since duplicate copies are created.

• Not Available for Image Copies: Duplexing is supported only for backup sets, not image copies.

• Number of Copies: RMAN supports duplexing for up to 4 copies.

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Key Notes

• Default Configuration: By default, RMAN creates only one copy of each backup piece unless duplexing is explicitly configured.

• Persistent Configuration: You can configure duplexing persistently for future backups:

  
  CONFIGURE BACKUP COPIES FOR DEVICE TYPE DISK TO 2;
  

  This ensures that all subsequent backups to disk will automatically create two copies.