When working with customers who are applying compression and/or encryption to their Oracle DB backups, I found that it isn't always clear if backups are compressed or encrypted. In this blog post I will break compression and encryption of Oracle backups down into the levels where these operations could occur. Below is a high level view of these 3 levels.
Database
Compression
Data in the database can be compressed in any one of the following formats or all of the formats
HCC - Available only on Exadata, or ZFS storage, this compression is a columnar compression format with different options that allow you to choose the appropriate access speed and compression ratio for your data
Advanced Compression - A licensable option that will automatically compress data in the background to optimize storage without compromising performance.
Basic Compression - Requires a lock on object during insert and is typically used within a data warehouse.
External Compression - In some cases the data stored in the database may already be compressed externally. An example of this is image files which are already stored in a compressed format.
Encryption
Data in the database can be encrypted in any one of the following formats or all of the formats
TDE - All data in the tablespace is encrypted by database.
Column Encryption - Specific data within a column is encrypted, SSN for example. This is less widely used and most customers use TDE instead.
External Encryption - In some cases the data stored in the database may already be encrypted by the application.
NOTE:
1. If the data is compressed and/or encrypted in these manors it will continue in that format when backed up.
- Any data that encrypted in the database will remain encrypted in the backups
- Any data that is compressed in the database will remain compressed in the backups
- Backups of data that is compressed and/encrypted will get little to no compression when backed up
2. RMAN does not know that the data is either compressed or encrypted, and querying the RMAN views will not tell you that either has occurred.
3. Having data encrypted and/or compressed in the database does not stop you from further compressing and/or encrypted the backups.
ZDLRA
Compression
Datafile Compression - With Datafile compression you have 2 choices to compress the backups
- RA_FORMAT = TRUE - This compresses all datafile backups in the new ZDLRA 23.1 format. If the datafile is part of a TDE tablespace, the blocks will be decrypted prior to compression to ensure the best compression ratio.
- RA_FORMAT not set or FALSE - Backups of datafiles will be sent as uncompressed (unless you create a RMAN compressed backupset). Once they are received on the ZDLRA they will be compressed in storage on ZDLRA. When replicated to another ZDLRA, or restored, they are uncompressed.
Real-time Redo Compression - When sending real-time redo to the ZDLRA you can have the ZDLRA create an RMAN compressed backupset for the archive logs. The level of compression can be set on the policy. Once stored in an RMAN compressed backupset format, it is replicated and restored as a compressed backupset.
SPFILE, Controfile, archivelog backups - The ZDLRA will NOT attempt to compress these backupsets internally. Only datafile backups are compressed on the ZDLRA.
Encryption
Datafile Encryption - Whether a datafile is encrypted by the ZDLRA in the new ZDLRA 23.1 format depends on these 2 conditions.
- RA_FORMAT = TRUE and "RMAN Encryption ON" - If the datafile is NOT part of a TDE tablespace, this will force BOTH compression and encryption of that datafile backup.
- RA_FORMAT = TRUE and "RMAN Encryption OFF" - If the datafile is part of a TDE tablespace, the backup of this datafile will remain encrypted. If the datafile is NOT part of a TDE tablespace, the backup will NOT be encrypted.
Real-time Redo Encryption - If real-time redo is utilized and your database has implemented TDE, the change data in the archive log backups will be encrypted. However, this backup is not considered RMAN encrypted, and ENCRYPTION=ENABLED must be set on the destination definition to ensure that the real-time redo backupsets are fully encrypted.
SPFILE, Controlfile, archivelog backup Encryption - These are not encrypted by the ZDLRA.
NOTE:
1. The new Space Efficient Encrypted backup feature of the ZDLRA only affects datafile backups.
2. Real-time redo backups can be compressed and/or encrypted by the ZDLRA.
3. If you are using the new RA_FORMAT=TRUE for non-TDE datafile backup, you will only get a compressed a backupset. You have set RMAN Encryption on with RA_FORMAT=TRUE in order to encrypt the backupset.
4. If you are backing up a non-TDE datafile, and wish to encrypt it with the library, it will also be compressed. You cannot encrypt without compression, but you can compress without encryption.
5. If datafile backups are sent to the ZDLRA without RA_FORMAT=TRUE, they will appear as compressed in the RMAN catalog. With RA_FORMAT=TRUE they will not appear as compressed.
6.If real-time redo is sent to the ZDLRA, and the profile for the database is set to compress the archivelogs, they will appear as compressed in the RMAN catalog.
RMAN
Compression
Datafile Compression - With Datafile compression you have 2 choices to compress the backups
- RA_FORMAT = TRUE - RMAN compression is ignored when this option is set.
- RA_FORMAT not set or FALSE - RMAN can create a compressed backupset for datafiles. If the datafile is part of a TDE tablespace, this datafile will not be able to create a virtual full. If the Datafile is NOT part of a TDE tablespace, the backset will be decompressed on the ZDLRA and will not be stored as a Compressed backupset.
SPFILE, Controfile, archivelog backups - The ZDLRA will NOT attempt to compress these backupsets internally. They remain compressed.
Encryption
Datafile Encryption - RMAN Encrypt ON creates an Encrypted backupset which cannot be virtualized by the ZDLRA. This should only be set when using RA_FORMAT=TRUE which bypasses RMAN encryption
SPFILE, Controlfile, archivelog backup Encryption - These can be encrypted by setting RMAN Encryption on.
NOTE:
1. The new Space Efficient Encrypted backup feature of the ZDLRA only affects datafile backups.
2. Real-time redo backups can be compressed and/or encrypted by the ZDLRA.
3. If you are using the new RA_FORMAT=TRUE for non-TDE datafile backup, you will only get a compressed a backupset. You have set RMAN Encryption on with RA_FORMAT=TRUE in order to encrypt the backupset.
4. If you are backing up a non-TDE datafile, and wish to encrypt it with the library, it will also be compressed. You cannot separate encryption from compression, but you can compress only.
