When an incremental backup is performed, the system is scanned for an existing change journal on each volume that it intends to back up. If a journal exists, the agent queries the registry for the journal’s ID and starting sequence number. This information will have been entered there by a previous master backup. If the entries exist, then the agent performs the following checks:
• A check to determine if the journal ID in the registry matches the ID of the volume’s current journal. If the IDs do not match, this indicates that the journal that existed during the master backup was deleted and that a new journal was created.
• A check to determine if the starting sequence number in the registry matches that of the volume’s current journal. If these numbers do no match, this indicates that the journal was filled to capacity with entries and has ‘wrapped’ around to the beginning. In this case, there will be file modifications that were made to the volume that are not recorded in the journal.
If both these checks succeed, then the agent uses the change journal to determine which files to include in the backup. If one of these checks fails, the agent does not use the journal and reverts to the volume scanning method. In this case, the agent includes some information in the backup output to warn the user that a new master backup must be completed in order to use the journal for subsequent incremental backups.