399.Which of the following is not an advantage of block media recovery (BMR)?
A. Reduced MTTR.
B. Datafiles remain offline while corrupt blocks are repaired.
C. Datafiles remain online while corrupt blocks are repaired.
D. A and C
Answer: B
答案解析：
根据
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Lowers the mean time to recover (MTTR) because only blocks needing recovery are restored and recovered
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Enables affected data files to remain online during recovery
block media recovery
The recovery of specified blocks within a data file with the Recovery Manager RECOVER ... BLOCK command. Block media recovery leaves the affected data files online and restores and recovers only the damaged or corrupted
blocks.
Purpose of Block Media Recovery
You can use block media recovery to recover one or more corrupt data blocks within a data file. Block media recovery provides the following advantages over data file media recovery:
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Lowers the mean time to recover (MTTR) because only blocks needing recovery are restored and recovered
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Enables affected data files to remain online during recovery
Without block media recovery, if even a single block is corrupt, then you must take the data file offline and restore a backup of the data file. You must apply all redo generated for the data file after the backup was created. The entire file is unavailable until media recovery completes. With block media recovery, only the blocks actually being recovered are unavailable during the recovery.
Block media recovery is most useful for physical corruption problems that involve a small, well-known number of blocks. Block-level data loss usually results from intermittent, random I/O errors that do not cause widespread data loss, and memory corruptions that are written to disk. Block media recovery is not intended for cases where the extent of data loss or corruption is unknown and the entire data file requires recovery. In such cases, data file media recovery is the best solution.