When you turn on logging for smart large objects, you must perform a level-0 backup of the sbspace.
Figure 60 shows what happens if you turn on logging in an sbspace that is not backed up. The unlogged changes to smart large object LO1 are lost during the failure, although the logged changes are recoverable. You will not be able to fully restore LO1.
During fast recovery, the database server rolls forward all committed transactions for LO1. If LO1 is unlogged, the database server would be unable to roll back uncommitted transactions. Then the LO1 contents would be incorrect. For more information, refer to Fast Recovery.