Reserved Space
Next in importance to the recovery window goal is the reserved_space parameter of DBMS_RA.ADD_DB and DBMS_RA.UPDATE_DB. The reserved space defines the amount of disk space guaranteed to each protected database to meet its recovery window goal.
Note:
This is the only storage parameter that is specified in ADD_DB rather than in the protection policy.
Because backups need space, you must estimate how much reserve space you believe is needed to store backups. For example, you might allocate 1024 GB of reserved space to the DB1124 database, which means the Recovery Appliance guarantees 1024 GB to DB1124 if the database needs this amount to meet its recovery window goal. The following graphic shows a section of a Protected Database Details report:
In the preceding example, the disk recovery window goal for DB1124 is 3 days, and the actual recovery window (the time to which the Recovery Appliance can currently recover) is 4.59 days. Meeting the recovery window goal requires 182.3 GB of backup data. This amount is less than 20% of the specified reserved space setting of 1024 GB. By default, at any given time, a database may actually have more or less than its specified reserved space available.
Note:
Reserved space is measured in space (GB), whereas the recovery window goal is measured in time.
The Recovery Appliance uses recovery window goals and reserved space settings to allocate storage dynamically to meet business requirements. If the Recovery Appliance has purged as much backup data as possible while still meeting the recovery window goal for each database, and if more space is needed, then the Recovery Appliance evaluates the reserved space setting of each database. Recovery Appliance purges backups for the database whose backups exceed the reserved space by the highest percentage, and logs a message in the RA_INCIDENT_LOG view. Query the RA_PURGING_QUEUE view to determine which database will next have a backup purged.
The ESTIMATE_SPACE procedure can assist with determining reserved space. When calculating reserved space for a compliance protection policy, the target_window should be the RECOVERY_WINDOW_COMPLIANCE plus an extra day for edge conditions.