Topic : RMAN

Command to delete archive logs older than 7days?


Answer :

RMAN> delete archivelog all completed before sysdate-7;

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How to view the current defaults for the database in RMAN?


Answer :

RMAN> show all;

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What is the use of crosscheck command in RMAN?


Answer :

Crosscheck will be useful to check whether the catalog information is intact with OS level information. This command only updates repository records with the status of the backups.
e.g. If user removes archived logs from disk with an operating system command; the repository still indicates that the logs are on disk; when in fact they are not.

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What are the differences between crosscheck and validate commands?


Answer :

Validate command is to examine a backup set and report whether it can be restored. RMAN scans all of the backup pieces in the specified backup sets and looks at the checksum to verify that the contents are intact so that backup can be successfully restored if necessary.
Crosscheck command is to verify the status of backups and copies recorded in the RMAN repository against media such as disk or tape. The crosscheck command only processes files created on the same device type as the channel running crosscheck.

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Which one is good; differential (incremental) backup or cumulative (incremental) backup?


Answer :

A differential backup; which backs up all blocks changed after the most recent incremental backup at level 1 or 0
RMAN> BACKUP INCREMENTAL LEVEL 1 DATABASE;
A cumulative backup; which backs up all blocks changed after the most recent incremental backup at level 0
RMAN> BACKUP INCREMENTAL LEVEL 1 CUMULATIVE DATABASE;
Cumulative backups are preferable to differential backups when recovery time is more important than disk space; because during recovery each differential backup must be applied in succession. Use cumulative incremental backups instead of differential; if enough disk space is available to store cumulative incremental backups.
This is command for taking Level 0 backup.
RMAN> BACKUP INCREMENTAL LEVEL 0 DATABASE;

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