Archived redo log files of the database do not have the same size as the online redo logs.
Cause is a generic behaviour of Oracle7.
In Oracle online redo log files are used in a circular fashion. The default for a R/3 installation is to have four online redo log files (log file groups, to be more precise; here it's sufficient to just think of each group to consist of one file only, i. e. no mirroring of online redo logs) with a size of 20MB each.
The database will write to one file, once that has been filled up, it will switch to the 2nd., 3rd., 4th. and then reuse the 1st. and so on.
The database ARCHive process will save the online redo logs to an archive directory (usually ORACLE_HOME/saparch) before they are reused (if the database runs in archive mode).
If the online redo log was fully written, the archived redo log will have the same size as the online redo log.
It is possible to force the database to switch from one online redo log to the next, before the online redo log file was completely filled with redo data, e. g. the database may have written 8MB of redo data to an online redo log file with a size of 20MB, and then an online redo log file switch may have been forced.
In this case the archived redo log file will have a size of 8MB only, i. e. the size of the archived redo log file is less than the size of the online redo log file. The archived file will always have the size of the amount of redo data kept in the online redo log file.
An online redo log switch is forced, for example, at the end of an online database backup using SAPDBA - brbackup.
No solution, generic behaviour, not an error
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