053试题 334/682 - crosscheck
题目：
334.What command would you use to ensure that backup records in the control file are pointing to actual
physical files on the backup media?
A. crosscheck
B. list backup
C. confirm
D. resync
E. backup validate
参考答案 A
解析
题目意思问，哪个命令，确认了备份记录在控制文件中，并且实际的备份的文件也存在。 crosscheck命令。选择A 。
参考文档：
https://docs.oracle.com/cd/E11882_01/backup.112/e10642/rcmmaint.htm#BRADV8171
Crosschecking the RMAN Repository
To ensure that data about backups in the recovery catalog or control file is synchronized with corresponding data on disk or in the media management catalog, perform a crosscheck. The CROSSCHECK command operates only on files that are currently recorded in the RMAN repository.
If you use a fast recovery area, backup retention policy, and archived redo log deletion policy, then you should not need to perform crosschecks very often. If you delete files by means other than RMAN, then you should perform a crosscheck periodically to ensure that the repository data stays current.
About RMAN Crosschecks
Crosschecks update outdated RMAN repository information about backups whose repository records do not match their physical status. For example, if a 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.
Figure 12-1 illustrates a crosscheck of a media manager. RMAN queries the RMAN repository for the names and locations of the four backup sets to be checked. RMAN sends this information to the target database server, which queries the media management software about the backups. The media management software then checks its media catalog and reports back to the server that backup set 3 is missing. RMAN updates the status of backup set 3 to EXPIRED in the repository. The record for backup set 3 is deleted once you run DELETE EXPIRED.
Figure 12-1 Crosschecking a Media Manager
Description of "Figure 12-1 Crosschecking a Media Manager"
Crosschecks are useful because they can do the following:
Update outdated information about backups that disappeared from disk or tape or became corrupted
Update the repository if you delete archived redo logs or other files with operating system commands
Use the crosscheck feature to check the status of a backup on disk or tape. If the backup is on disk, then CROSSCHECK checks whether the header of the file is valid. If a backup is on tape, then the command checks that the backups exist in the media management software catalog.
Backup pieces and image copies can have the status AVAILABLE, EXPIRED, or UNAVAILABLE. You can view the status of backups by running the RMAN LIST command or by querying V$BACKUP_FILES or recovery catalog views such as RC_DATAFILE_COPY or RC_ARCHIVED_LOG. A crosscheck updates the RMAN repository so that all of these techniques provide accurate information. RMAN updates each backup in the RMAN repository to status EXPIRED if the backup is no longer available. If a new crosscheck determines that an expired backup is available again, then RMAN updates its status to AVAILABLE.
Oracle Database Backup and Recovery Reference for
CROSSCHECKsyntax and a description of the possible status valuesOracle Database Backup and Recovery Reference for
DELETEsyntax
END
-- 2019-09-12 add
题目：
682. Identify the scenarios in which the RMAN CROSSCHECR command is useful. (Choose all that apply.)
A.To check that the obsolete backups are deleted from the repository records and from the disk.
B.To update the RMAN repository if you delete archived redo logs with operating system commands.
C.To update outdated information about backups that disappeared from disk or tape or became corrupted and inaccessible.
D.To synchronize the actual files on disk or in the media management catalog with the RMAN repository for which the backup was not taken using RMAN.
参考答案 AD （有误，争取的答案应该是BC ）
解析
那些场景下，crosscheck 命令有用。
选项A ，是report命令干的事情。
选项D，是命令sync干的事情。
参考文档，参考上面的题目的文档。
END
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