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1#
发表于 2013-1-3 17:40:29
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查看: 5161 |
回复: 5
看到11.1官方文档中有如下一段话,红色的字没有看懂,求解答,谢谢。
For the purposes of a backup retention policy based on redundancy, a backup set is counted as one instance of a backup. This statement is true even if there are multiple copies of the backup pieces that make up backup set, such as when a backup set has been backed up from disk to tape.
For the purposes of a recovery window retention policy, either all of the copies of a backup set are obsolete, or none of them are.
This point is easiest to grasp when viewing the output of the LIST and REPORT commands.
To view the effect of a backup retention policy on backups of backups:
Back up a datafile.
The following example backs up datafile 5:
BACKUP AS BACKUPSET DATAFILE 5;
Run the LIST command for the datafile backup in the preceding step.
For example, run the following command (sample output included).
LIST BACKUP OF DATAFILE 5 SUMMARY;
List of Backups
===============
Key TY LV S Device Type Completion Time #Pieces #Copies Compressed Tag
------- -- -- - ----------- --------------- ------- ------- ---------- ---
18 B F A DISK 04-AUG-07 1 1 NO TAG20070804T160 134
Use the backup set key from the previous step to back up the backup set.
For example, enter the following command:
BACKUP BACKUPSET 18;
Run the same LIST command that you ran in step 2.
For example, run the following command (sample output included).
LIST BACKUP OF DATAFILE 5 SUMMARY;
List of Backups
===============
Key TY LV S Device Type Completion Time #Pieces #Copies Compressed Tag
------- -- -- - ----------- --------------- ------- ------- ---------- ---
18 B F A DISK 04-AUG-07 1 2 NO TAG20070804T160 134
Only one backup set is shown in this output, but there are now two copies of it.
Generate a report to see the effect of these copies under a redundancy-based backup retention policy.
For example, issue the following command:
REPORT OBSOLETE REDUNDANCY 1;
None of the copies is reported as obsolete because both copies of the backup set have the same values for set_stamp and set_count.
Generate a report to see the effect of these copies under a recovery window-based backup retention policy.
For example, issue the following command:
REPORT OBSOLETE RECOVERY WINDOW 1 DAY;
None of the copies of the backup set is reported as obsolete or based on the CHECKPOINT_CHANGE# of this backup set, with respect to the current time and the availability of other backups.
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