Which of the following are correct about block media recovery? (Choose all that apply.)
A.
Physical and logical block corruption is recorded automatically in V$DATABASE_BLOCK_CORRUPTION.
B.
Logical corruptions are repairable by BMR.
C.
Physical corruptions are repairable by BMR.
D.
RMAN can use any backup for a BMR restore.
E.
ARCHIVELOG mode is not required if you have both a full and incremental backup for restore.
Explanation:
Overview of Block Media Recovery (link)
Basic Concepts of Block Media Recovery
Whenever block corruption has been automatically detected, you can perform block media recovery manually
with the RECOVER … BLOCK command. By default, RMAN first searches for good blocks in the real-time
query physical standby database, then flashback logs and then blocks in full or level 0 incremental backups.
Identification of Corrupt Blocks
The V$DATABASE_BLOCK_CORRUPTION view displays blocks marked corrupt by database components
such as RMAN, ANALYZE, dbv, and SQL queries. The following types of corruption result in the addition of
rows to this view: Physical corruption (sometimes called media corruption) The database does not recognize
the block: the checksum is invalid, the block contains all zeros, or the block header is corrupt. Physical
corruption checking is enabled by default. You can turn off checksum checking by specifying the
NOCHECKSUM option of the BACKUP command, but other physical consistency checks, such as checks of
the block
headers and footers, cannot be disabled.
The block has a valid checksum, the header and footer match, and so on, but the contents are logically
inconsistent. Block media recovery may not be able to repair all logical block corruptions. In these cases,
alternate recovery methods, such as tablespace point-in-time recovery, or dropping and re-creating the affected
objects, may repair the corruption. Logical corruption checking is disabled by default. You can turn it on by
specifying the CHECK LOGICAL option of the BACKUP, RESTORE, RECOVER, and VALIDATE commands.
The database can detect some corruptions by validating relationships between blocks and segments, but
cannot detect them by a check of an individual block. The V$DATABASE_BLOCK_CORRUPTION view does
not record at this level of granularity.
Prerequisites for Block Media Recovery (link)
The following prerequisites apply to the RECOVER … BLOCK command:
The target database must run in ARCHIVELOG mode and be open or mounted with a current control file.
If the target database is a standby database, then it must be in a consistent state, recovery cannot be in
session, and the backup must be older than the corrupted file.
The backups of the data files containing the corrupt blocks must be full or level 0 backups and not proxy copies.
If only proxy copy backups exist, then you can restore them to a nondefault location on disk, in which case
RMAN considers them data file copies and searches them for blocks during block media recovery.
RMAN can use only archived redo logs for the recovery. RMAN cannot use level 1 incremental backups. Block
media recovery cannot survive a missing or inaccessible archived redo log, although it can sometimes survive
missing redo records.
Flashback Database must be enabled on the target database for RMAN to search the flashback logs for good
copies of corrupt blocks.
If flashback logging is enabled and contains older, uncorrupted versions of the corrupt blocks, then RMAN can
use these blocks, possibly speeding up the recovery. The target database must be associated with a real-time
query physical standby database for RMAN to search the database for good copies of corrupt blocks.