text: FlashCopy includes the FlashCopy function, Global Mirror with change volumes, and 
  active-active (HyperSwap) relationships. 
  
  For multiple FlashCopy targets, you must consider the number of mappings. For example, for 
  a mapping with a grain size of 256 KiB, 8 KiB of memory allows one mapping between a 
  16 GiB source volume and a 16 GiB target volume. Alternatively, for a mapping with a 256 KiB 
  grain size, 8 KiB of memory allows two mappings between one 8 GiB source volume and two 
  8 GiB target volumes. 
  
  When creating a FlashCopy mapping, if you specify an I/O group other than the I/O group of 
  the source volume, the memory accounting goes toward the specified I/O group, not toward 
  the I/O group of the source volume. 
  
  When creating FlashCopy relationships or mirrored volumes, more bitmap space is allocated 
  automatically by the system, if required. 
  
  For FlashCopy mappings, only one I/O group consumes bitmap space. By default, the I/O 
  group of the source volume is used. 
  
  When you create a reverse mapping, such as when you run a restore operation from a 
  snapshot to its source volume, a bitmap is created. 