A data block lost write occurs when an I/O subsystem acknowledges the completion of the block write, while in fact the write did not occur in the persistent storage.

When the parameter is set to TYPICAL on the primary database, the instance logs buffer cache reads for read/write tablespaces in the redo log, which is necessary for detection of lost writes.

When the parameter is set to FULL on the primary database, the instance logs reads for read-only tablespaces and read/write tablespaces.

When the parameter is set to TYPICAL or FULL on the standby database or on the primary database during media recovery, the instance performs lost write detection.

When the parameter is set to NONE on either the primary database or the standby database, no lost write detection functionality is enabled.