ocp 053
688. Which two statements are true about the compressed backups in RMAN? (Choose two.)
A.Compressed backups can only be taken on the tape drives.
B.The binary compression creates some performance overhead during backup operation.
C.The ZLIB compression algorithm can be used only if the COMPATIBLE in itialization parameter is set to 11.1.0.
D.The media manager compression for the tape drive should be enabled for taking compressed backups on the tape.
Answer: BD
答案解析：
A错，也可以备份在disk上。
C错， only if the COMPATIBLE in itialization parameter is set to 11.1.0，应该是11.0.0或者以上
sys@TEST0221> select ALGORITHM_NAME,ALGORITHM_COMPATIBILITY,ALGORITHM_DESCRIPTION from v$rman_compression_algorithm
2 /
ALGORITHM_NAME ALGORITHM_COMPATIB ALGORITHM_DESCRIPTION
---------------------------------------------------------------- ------------------ ----------------------------------------------------------------
BZIP2 9.2.0.0.0 good compression ratio
BASIC 9.2.0.0.0 good compression ratio
LOW 11.2.0.0.0 maximum possible compression speed
ZLIB 11.0.0.0.0 balance between speed and compression ratio
MEDIUM 11.0.0.0.0 balance between speed and compression ratio
HIGH 11.2.0.0.0 maximum possible compression ratio
6 rows selected.
本机测试：竟然没有ZLIB
16:23:29 SYS@db252>col ALGORITHM_NAME for a40
16:23:45 SYS@db252>col ALGORITHM_NAME for a10
16:23:57 SYS@db252>col ,ALGORITHM_DESCRIPTION for a40
16:24:12 SYS@db252>select ALGORITHM_NAME,ALGORITHM_COMPATIBILITY,ALGORITHM_DESCRIPTION from v$rman_compression_algorithm;
ALGORITHM_ ALGORITHM_COMPATIB ALGORITHM_DESCRIPTION
---------- ------------------ ----------------------------------------------------------------
BASIC 9.2.0.0.0 good compression ratio
LOW 11.2.0.0.0 maximum possible compression speed
MEDIUM 11.0.0.0.0 balance between speed and compression ratio
HIGH 11.2.0.0.0 maximum possible compression ratio
Elapsed: 00:00:00.02
16:24:13 SYS@db252>