When a read or write operation is requested to an area of the target volume that has not yet been copied, old data in the source volume is copied to the target volume first.
The following figures show the process flow.
Figure. On-demand copy when there is a read request to an area of the target volume not yet copied
Figure. On-demand copy when there is a write request to an area of the target volume not yet copied
- There is a read request or write request to the area in the S-VOL or T-VOL where the data has not been copied.
- When a read or write is made to the area in the S-VOL or T-VOL where the data has not been copied, Compatible FlashCopy® V2 performs on-demand copying. The data is copied from the S-VOL to the T-VOL.
- When on-demand copying is complete, Compatible FlashCopy® V2 performs the read or write operation.
On-demand copying might not always be executed when there is a read request to the area in the S-VOL or T-VOL. In this case, the host reads the source volume, not the target volume.