When you archive the offline redo log files with BRARCHIVE, performing software compression in advance is useless, since the previously determined compression rates cannot be used for archiving the next redo log files. If BRARCHIVE does not have any information on the compression rates, the default value of 1 is assumed. This means, for example, that when the tape size is 1600 MB and the redo log files are 20 MB, up to 80 offline redo log files can be archived on a volume.
If, however, a larger number of offline redo log files were written on one day that actually fit on the tape, you can change the parameter tape_size accordingly.
Consider the following: We know from experience that during a hardware compression, the size of the offline redo logs shrinks by around a third. Therefore, you can increase the init<DBSID>.sap parameter tape_size by around 50% (to 2400 MB in the above example), thus reflecting the actual compression rate. This enables you to archive many more (up to 120 in the example) offline redo log files with one BRARCHIVE call.
You can define a separate init<DBSID>.sap profile parameter, tape_size_arch, for BRARCHIVE. If you do this, changes to individual parameters do not affect the next database backup with BRBACKUP.