Introducing Arcserve Backup Agents and Options › Using Agents › Agent for Open Files › Introducing the Agent › The Data Integrity Problem › File Synchronization

File Synchronization

The <aof> solves the data integrity problem by ensuring that when a backup client attempts to open a file, access is not granted until the agent is satisfied that the file is in a good state to be backed up. To do so, the agent does the following:

1. The agent searches for a period of time during which no applications are writing to the file. This period of time is known as the Write Inactivity Period and is typically set to five seconds.
2. After the Write Inactivity Period has been found, the agent establishes that the file is stable, and it allows the backup process to continue. The file is now synchronized.
3. After a file is synchronized, applications can write to the file, but the agent ensures that the backup client receives the file data as it was at the time of synchronization. To accomplish this, when an application attempts to write to a synchronized file, the agent creates a copy of the data that is about to be changed before allowing the write to occur. This private copy of the data, called the preview data, is sent to the backup client when the backup is made, ensuring that the file remains synchronized. Thus, applications can continue to write to synchronized files while a backup is taking place without jeopardizing the integrity of the file.
4. The agent also accumulates preview data if a file being backed up is opened by an application after the backup has started. In this situation, synchronization occurs at the point when the application opens the file.