401.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$DATABASE_BLOCK_
CORRUPTION.
B. Logical corruptions are repairable by BMR.
C. Physical corruptions are repairable by BMR.
D. RMAN can use any backup for a BMR restore.
E. ARCHIVELOG mode is not required if you have both a full and incremental backup for restore.
Answer: AC
In most cases, the database marks a block as media corrupt and then writes it to disk when the
corruption is first encountered. No subsequent read of the block will be successful until the block is
recovered. You can only perform block recovery on blocks that are marked corrupt or fail a
corruption check. Block media recovery is performed using the RMAN RECOVER...BLOCK
command. By default, RMAN searches the flashback logs for good copies of the blocks, and then
searches for the blocks in full or level 0 incremental backups. When RMAN finds good copies, it
restores them and performs media recovery on the blocks.
Block media recovery can only use redo
logs for media recovery, not incremental backups.
The V$DATABASE_BLOCK_CORRUPTIONview displays blocks marked corrupt by database
components such as RMAN commands, ANALYZE, dbv, SQL queries, and so on. The following
types of corruption result in rows added to this view:
• Physical/Media corruption: The database does not recognize the block: the checksum is
invalid, the block contains all zeros, or the block header is fractured. Physical corruption
checking is enabled by default.
• Logical corruption: The block has a valid checksum, the header and footer match, but the
contents are inconsistent. Block media recovery cannot repair logical block 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