text: With this configuration, use a copyrate equal to 0 only. In this state, the virtual capacity of the 
  target volume is identical to the capacity of the source volume, but the real capacity (the one 
  that is used on the storage system) is lower, as shown on Figure 11-15. The real size of the 
  target volume increases with writes that are performed on the source volume, on not already 
  copied grains. Eventually, if the entire source volume is written (unlikely), the real capacity of 
  the target volume is identical to the source’s volume. 