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Best Practices for Oracle 11g Backup and Recovery using RMAN and Dell EqualLogic Snapshots
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During a level 1 incremental backup and onwards, RMAN verifies every block in the data files to detect
if any modifications have occurred since the previous incremental backup. If there are modifications,
then only the blocks containing modifications will be copied. As a result, size of incremental backups
(level 1 and onwards) is typically much less than level 0 or full backups.
Even though level 1 backup and incremental backups after level 1 were smaller in size, the time taken
to complete those backups was almost same as level 0 or full backup. This is because RMAN will have
to verify every block in the data files to identify if any modifications have occurred. This is the main
drawback of this approach as it significantly increases the backup window, extending the RMAN
processing impact on production database servers.
4.2.2 Performance impact: RMAN incremental backup
System performance impacts similar to those seen in the full backup test in Section 4.1.2 (CPU
utilization, response time, TPS) were observed during the incremental backup tests.
4.2.3 Database complete recovery time
For the incremental recovery time test we ran the Quest Benchmark factory TPC-C style workload on
the production database for six hours. At the beginning of the 6 hour period we created the level 0
incremental backup. Then approximately one-half way through the test period we created a level 1
incremental backup. Then we continued running the workload on the database to the end of the 6
hour test period. At that point, we initiated a restore/recovery process.
Timing results for incremental restore/recovery:
• Time to restore the database: 45 minutes
• Time to recover the database: 31 minutes
• Total time: 76 minutes
When comparing these results to the results in 4.1.3 for an RMAN full backup restore/recovery process
you see that the recovery process took much less time (31 minutes vs. 106 minutes). The total time for
the restore/recovery process was reduced from 151 minutes to 76 minutes.
These results show that use of incremental backups can significantly reduce the time to perform
complete recovery of the database. But the drawback with this approach is that you increase the total
amount of time that RMAN is running on the system. As illustrated in Section 4.1.2, this can have a
significant impact on CPU resources, and thus may not be acceptable for many larger database
environments.