HP XP7 Storage - Manual (Page 10)

If there is a request for a write operation to an S-VOL in which the requested data is not yet copied
to the target, or a request for a read/write operation to a T-VOL in which the requested data is
not yet copied, the old data is copied from the S-VOL to the T-VOL first, and then the read/write
operation is performed. This process is called on-demand copying. The following figures show the
process of on-demand copying.
Figure 3 On-demand copy (case 1: write request to an area in the S-VOL from which the data has
not been copied)
Figure 4 On-demand copy (case 2: Read request to an area in the T-VOL to which the data has not
been copied)
10 About Compatible FlashCopy