The Symantec Backup Exec Advanced Open File Option (AOFO) uses advanced open file and image technologies designed to alleviate issues that are sometimes encountered during backup operations, such as protecting open files and managing shortened backup windows.
When a job is submitted for backup with the AOFO selected, a snapshot of each volume is created, providing a point-in-time record of the data. When creating a snapshot, Backup Exec uses snapshot technologies to momentarily suspend write activity to a volume so that a snapshot of the volume can be created.
If the files selected for backup reside on more than one volume, by default Backup Exec creates a snapshot for each volume that contains data to be backed up. For example, if the data to be backed up resides on a single volume, a single snapshot is created. If data resides on four volumes, four snapshots are created. After creating a snapshot, the data is backed up from the snapshots, and then the snapshots are deleted.
During the backup job, files can be opened, and data can change. AOFO allows data to change by making a copy of the original data, named a cache file. The snapshot tracks the data changes, as illustrated in the cache file diagram.
When the snapshot comes to a changed block, it replaces the changed block with the original data from the cache file. The snapshot sends the point-in-time data to Backup Exec. The data is then written to tape or disk.
Symantec strongly recommends that Backup Exec database agents be used to back up databases. Backup Exec database agents provide selective restores of data and more integration with the database application while preventing backups of partial transactions. Agents also enable backups on a database that is spread across multiple disk volumes.
You can use AOFO on the same volume as a database to provide open file support for other applications. AOFO provides generic protection for flat files when Backup Exec agents are not used, and provides protection for Microsoft Outlook PST files.