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Minimizing Backup Load and Duration
When using DURATION you can run the backup with the maximum possible performance, or run as slowly as possible while still finishing within the allotted time, to minimize the performance impact of backup tasks. To maximize performance, use the MINIMIZE TIME option with DURATION, as shown in Example 10-4.
Example 10-4 Using MINIMIZE TIME with BACKUP DURATION
BACKUP DURATION 4:00 PARTIAL MINIMIZE TIME DATABASE FILESPERSET 1;
To extend the backup to use the full time available, use the MINIMIZE LOAD option, as in Example 10-5.
Example 10-5 Using MINIMIZE LOAD with BACKUP DURATION
BACKUP DURATION 4:00 PARTIAL MINIMIZE LOAD DATABASE FILESPERSET 1;
In Example 10-5, RMAN monitors the progress of the running backup, and periodically estimates how long the backup takes to complete at its present rate. If RMAN estimates that the backup will finish before the end of the backup window, then it slows down the rate of backup so that the full available duration is used. This reduces the overhead on the database associated with the backup.
Note these issues when using DURATION and MINIMIZE LOAD with a tape backup:
- Efficient backup to tape requires tape streaming. If you use
MINIMIZE LOAD, then RMAN may reduce the rate of backup to the point where tape streaming is not optimal. - RMAN holds the tape resource for the entire duration of the backup window. This prevents the use of the tape resource for any other purpose during the backup window.
Because of these concerns, it is not recommended that you use MINIMIZE LOAD when backing up to tape.