For a snapshot high-speed backup using OPC, the entire transaction volume must be copied to the backup volume every time the backup is started. However, as long as the same transaction volume and backup volume are being used, the entire transaction volume need not be physically copied every time OPC is run. Instead, physically copying only the data that has been modified since the start of the previous backup can create a complete snapshot image. This can greatly reduce the time taken for physical copying.
The QuickOPC function achieves this by copying only the data that has been changed from the point of the previous physical copy.
The snapshot high-speed backup using the QuickOPC function is referred to as the differential snapshot high-speed backup.
The conventional snapshot high-speed backup and the differential snapshot high-speed backup are compared below:
Point
When the QuickOPC function is used, the hardware records the changes that are made to the copy source and destination after completing the OPC logical copy. The state in which the hardware keeps a record of changes is called "tracking state".
Figure 5.1 Comparison Between Conventional Snapshot High-speed Backup and Differential Snapshot High-speed Backup
