Which three statements are true about compression of backup sets?
A.
Compressed backups can only be written to media.
B.
Binary compression creates performance overhead during a backup operation.
C.
Unused blocks below the high-water mark are not backed up.
D.
Compressed backups cannot have section size defined during a backup operation
E.
It works only for locally managed tablespaces.
B,C,E
BCE
B, C, E
B?? not A because media and disk,
B Binary compression creates some performance overhead during backup and restore operations. Binary compression consumes CPU resources, so do not routinely schedule compressed backups when CPU usage is high.
BE correct A wrong. one correct still missing
B, C, E:
https://docs.oracle.com/cd/B19306_01/backup.102/b14194/rcmsynta009.htm#i1015382
and also from this link:
“RMAN also skips other datafile blocks that do not currently contain data, if all of the following conditions apply:
The COMPATIBLE initialization parameter is set to 10.2
There are currently no guaranteed restore points defined for the database
The datafile is locally managed
The datafile is being backed up to a backup set as part of a full backup or a level 0 incremental backup
The backup set is being created on disk.
“
BCE
https://docs.oracle.com/cd/E49329_01/backup.121/b71297/rcmbckba.htm#i1034440
https://docs.oracle.com/cd/E49329_01/backup.121/b71297/rcmcncpt.htm#CIHDGBJF
B,C,E
E – dictionary managed tablespaces stores freelist in system tablespace, so if database is down, RMAN is unable to skip unused blocks
Thus compression works only in locally managed tablespaces
BCE