If you use the incremental or the differential backup method as part of your backup strategy, Backup Exec must know when a file has been modified. Full backups include all of the data that you selected to back up. Subsequent incremental and differential backups back up only new files and any files that have changed.

Whenever a file is created or changed, a computer's file system notes and records the change. You can specify the method by which Backup Exec determines if a file needs to be backed up in the Files and Folders options when you create a backup job. Backup Exec uses the method that you choose to determine when a file is created or changed.

This topic includes the following information:

Modified time

Archive bit

Catalogs

How Backup Exec uses the change journal to determine which files have changed

Resolving change journal errors

Modified time

When Backup Exec runs a full backup or incremental backup job, the time that the backup job starts is recorded in the Backup Exec Database. Backup Exec adds the time of the backup job to the Backup Exec Database only if the full backup job completes successfully. The next time that you run an incremental backup job or a differential backup job, Backup Exec compares the file system time to the backup time. If the file system time is later than the time that is recorded in the database, the file is backed up. If the file's modified time is older than the previous backup's modified time, that file is not backed up. If the job does not complete successfully, subsequent differential or incremental backup jobs back up all of the data instead of only the data that has changed.

When you run an incremental backup job, Backup Exec records a new time in the Backup Exec Database. The database time is not updated for differential backup jobs.

When you select the modified time method, Backup Exec uses the Windows change journal to determine if a file has changed since the last time it was backed up. If the change journal is not available, Backup Exec compares the file information to the previous backup time to determine if the file has changed.

Using modified time lets Backup Exec run more accurate incremental backups or differential backups even if other processes have modified files' archive bits.

Archive bit

Backup Exec uses the archive bit from the file system to determine if a file has changed since the last time it was backed up.

When you use the archive bit, Backup Exec turns the archive bit off when a file is backed up. Turning off the archive bit indicates to Backup Exec that the file has been backed up. If the file changes again before the next backup job, the bit is turned on again. Backup Exec backs up the file in the next backup.

If the next backup job is a full backup job or an incremental backup job, the bit is turned off when the backup job completes. If the next backup job is a differential backup job, the archive bit is left intact.

Catalogs

Backup Exec compares path names, modified time, deleted and renamed files and folders, and other attributes. When you select the catalog method, Backup Exec uses the Windows change journal to determine if a file has changed since the last time it was backed up. If the change journal is not available, Backup Exec compares the file information to previous catalogs to determine if it has changed.

The catalog method is only available if the Advanced Disk-based Backup feature (ADBO) is installed.

See Configuring file and folder options for backup jobs.

How Backup Exec uses the change journal to determine which files have changed

When you choose the modified time backup method or the catalog backup method for files, Backup Exec uses the update sequence number (USN) change journal. Backup Exec scans the change journal to get a list of the changed files to back up, rather than scanning all files. Use of the change journal reduces the amount of time that Backup Exec requires to perform an incremental backup or a differential backup.

You cannot disable the use of the change journal for either the modified time backup method or the catalog backup method. If the change journal is not already enabled on the volume, then Backup Exec automatically enables it. The volume must support change journals. For example, NTFS and ReFS volumes support change journals, but FAT volumes do not.

When Backup Exec enables the change journal, it sets the change journal defaults as shown in Table: Change journal defaults set by Backup Exec. Backup Exec does not modify settings for a change journal that already exists.