The recovery journal holds redo and undo log buffers, which act as Assure MIMIX for AIX’s internal rollback window. If you are using external archive media such as tape, the size of the recovery journal is not critical to the ability to restore data. However, the larger the recovery journal, the larger the internal rollback window, which implies faster access to redo and undo logs during production restores in that window.
If you are not using external archive media, then the size of the recovery journal is critical for data protection. Rollbacks cannot extend beyond the logs that exist on the recovery server. You must estimate average throughput and calculate recovery journal area based on the length of the desired average restore window.
Throughput
Required internal rollback window