oracle: ocp题解与实验(5/205)

题目：

5. You are performing a block media recovery on the tools01.dbf data file
in the SALES database using RMAN. Which two statements are correct in this
scenario? (Choose two.)
A. You must ensure that the SALES database is mounted or open.
B. You must restore a backup control file to perform a block media
recovery.
C. You must take the tools01.dbf data file offline before you start a block
media recovery.
D. You must put the database in NOARCHIVELOG mode to perform a block media
recovery.
E. You can perform only a complete media recovery of individual blocks,
point-in-time recovery of individual data blocks is not supported.
Answer: A, E

题目翻译：你针对SALES数据库的tools01.dbf数据文件用RMAN做block media recovery，下面哪两个语句是正确的？

答案解释：

这是关于block media recovery的，看下官方资料：

Block Media Recovery

Block media recovery is a technique for restoring and recovering individual data blockswhile all database files remain online and available. If corruption is limited to only a few
blocks among a subset of database files, then block media recovery might be preferable to datafile recovery.

The interface to block media recovery is provided by RMAN. If you do not already use RMAN as your principal backup and recovery solution, then you can still perform block media recovery
by cataloging into the RMAN repository the necessary user-managed datafile and
archived redo log backups.

从这段描述就可以知道，这种block级别的恢复是RMAN工具提供的（其他手段也必须借用RMAN数据），并且数据库文件必须online和available，所以可以判断选项A是正确的，而C是错误的。段最后的红字，archived redo log backups表明是在archive模式下的可以知道D也是错误的。

上面是概要描述，再看RMAN中关于其的详细解释，注意红字：

BLOCKRECOVER

Purpose
Block media recovery recovers an individual data block or set of data blocks within a datafile.This type of recovery is useful if the data loss or corruption applies to a small number of
blocks rather than to an entire datafile.

Typically, block corruption is reported in error messages in trace files. Block-level data loss usually results from:

I/O errors causing minor data loss

Memory corruptions that get flushed to disk

You can either use

BLOCKRECOVER

CORRUPTION

LIST

to recover all blocks reported in the

V$DATABASE_BLOCK_CORRUPTION

view, or specify the datafile number and block number or the tablespace and data block address (DBA) when executing the

BLOCKRECOVER

command.

Restrictions and Usage Notes

The target database must be mounted or open.You donot have to take a datafile offlineif you are performing block media
recovery on it.

You can only perform complete media recovery of individual blocks. Point-in-time recovery of individual data blocks is not supported.

You can only perform block media recovery on corrupt blocks.

Blocks marked media corrupt are not accessible until recovery completes.

You cannot perform block media recovery when using a backup control file.

You cannot use proxy backups to perform block media recovery. If the only backups that you have are proxy backups, then you can restore them to a nondefault location on disk, which causes RMAN to view the restored files
as datafile copies. You can then use the datafile copies for block media recovery.

You must have a full backup of the file containing the corrupt blocks: block media recovery cannot use incremental backups.

If RMAN fails to access a specific archived redo log file needed for block media recovery, it performs restore failover, trying all other backups listed in the RMAN repository that are suitable for use in this operation,
and only fails if no suitable backup is available. See Oracle Database Backup and Recovery Advanced User's Guide
for details on restore failover.

Block media recovery cannot survive a missing or inaccessible archived log, although it can sometimes survive missing or inaccessible records (Oracle
Database Backup and Recovery Advanced User's Guide).

The datafile header block (block

1

) cannot be recovered.

You cannot perform block media recovery in

NOARCHIVELOG

mode.

读完这些红字，是否发现就是题目中的各个选项呢？因此答案是AE