When you back up the Oracle database with the Oracle Recovery Manager, the SAP backup library helps to optimize the utilization of fast tape drives by combining multiple data files in save sets. Multiple file access – also known as “file multiplexing” – maximizes the flow of data to keep tape drives in streaming mode.
For a preparation run, set the backup_dev_type parameter to rman_prep.
For an incremental backup with the SAP backup library, the saveset_members parameter is internally set to all so that only one “incremental save set” is created including all changed blocks.
The SAP backup library optimizes the distribution of the data files across the save sets in a preparation run as follows:
1. It estimates the expected compression of the save sets by using BRTOOLS to determine the compressed save set sizes.
2. BRBACKUP forms save sets and stores the information on the composition of the save sets and the compression rates for future backups in the database.
The following graphic shows this:
A save set can contain from one to four individual data files, all files of a tablespace, or the complete data backup. The size of the save sets for the backup must be selected according to the tape device. A fast data flow with a minimum save set size is the optimum. Large save sets are not recommended, since in a restore the complete save set has to be read, even if only one data file is required.
SAP recommends that you perform the preparation run once a month – using the BRBACKUP command –d|-device with the rman_prep parameter – and each time that major changes have been made to the database, for example after a reorganization, an SAP release change, database migration, or mass data import. After a tablespace extension, it is enough to execute the run for the newly created files only.
For more information, see RMAN-Relevant Profile Parameters.