1Z0-060 · Question #193
Which three statements are true about RMAN compressed backups?
The correct answer is B. Compressed backups can be written to media only if using proxy copies. C. File system compression should be enabled if compressed backups are being written to disk. E. Compression creates some performance overhead during backups to disk. RMAN compressed backups require proxy copies to reach tape media, benefit from file system compression on disk, and always incur CPU overhead at the server regardless of destination.
Question
Which three statements are true about RMAN compressed backups?
Options
- AMedia manager compression should not be enabled if compressed backups are being written to
- BCompressed backups can be written to media only if using proxy copies.
- CFile system compression should be enabled if compressed backups are being written to disk.
- DCompression creates some performance overhead during backups to tape.
- ECompression creates some performance overhead during backups to disk.
How the community answered
(15 responses)- A7% (1)
- B87% (13)
- D7% (1)
Why each option
RMAN compressed backups require proxy copies to reach tape media, benefit from file system compression on disk, and always incur CPU overhead at the server regardless of destination.
Avoiding media manager compression when RMAN compression is active is a best-practice recommendation to prevent double-compression CPU waste, not an inherent property of RMAN compressed backups; the statement is also truncated and cannot be evaluated as written.
When directing compressed backup sets to a media manager (tape), RMAN requires the proxy copy mechanism because the SBT channel streaming protocol cannot natively carry RMAN-compressed backup set structures; proxy copies let the media manager handle data movement directly.
When RMAN compressed backups are written to disk, enabling OS-level file system compression on the destination path allows the OS to apply an additional compression pass, further reducing the physical disk footprint of the backup pieces.
Compression overhead is not exclusive to tape - the CPU cost of the compression algorithm is borne by the database server process regardless of the I/O destination, so disk backups incur the same overhead, making this choice factually incomplete.
RMAN runs its configured compression algorithm (BZIP2, ZLIB, or LZO) inline during backup stream generation, consuming database server CPU and adding measurable elapsed time whether the backup destination is disk or tape.
Concept tested: RMAN compressed backup destination constraints and CPU overhead
Source: https://docs.oracle.com/en/database/oracle/oracle-database/19/bradv/backing-up-database.html
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