text: Figure 11-3 Copy on Write steps 
  
  With IBM FlashCopy, the target volume is immediately accessible for both Read*and*Write 
  operations. Therefore, a target volume can be modified, even if it is part of a FlashCopy 
  mapping. As shown in Figure 11-4, when a Write operation is performed on the*target*
  volume, the grain that contains the blocks to be changed is first copied from the source (*Copy*
  *on Demand*). It is then modified with the new value. The bitmap is modified so the grain from 
  the source is*not*copied again, even if it is changed or if a background copy is enabled. 