Restartability 

If a database failure occurs (due to a power failure for example) and if the devspaces are were fully functioning, the database system uses the log entries to restore the database instance to its last consistent state when the database instance is restarted.

This means that the effects which completed transactions had on the data devspaces are reproduced (rolled forward), and the effects that uncompleted transactions would have had are cancelled out (rolled back).

If there is an error in the data devspace (physical disk error), then all you have to do is to import the last complete data backup once the problem has been solved. If the log area still contains all the required data, the database system uses the log entries to restore the database instance to its last consistent state when the database instance is restarted.