To optimize recoverability, log files can be used to recover message transaction data if a hardware failure corrupts the information store or the directory database files, provided you have backed up the logs or the logs are intact. Log files are usually maintained on a physical disk drive separate from the information store and directory database files.
If database files are damaged, a backup can be restored and any data that has not been backed up but has been recorded in the transaction logs can be played back. These transactions are entered into the restored database file to bring the database up-to-date to the point in time where the database files were damaged.