text: The migration of volumes by using the volume copy feature requires more user interaction, 
  but might be a preferred option for particular use cases. One such example is migrating a 
  volume from a tier 1 storage pool to a lower performance tier 2 storage pool. 
  
  First, the volume copy feature can be used to create a copy in the tier 2 pool (steps 1 and 2). 
  All reads are still performed in the tier 1 pool to the primary copy. After the volume copies are 
  synchronized (step 3), all writes are destaged to both pools, but the reads are still only done 
  from the primary copy. 
  
  Now, the roles of the volume copies can be switched such that the new copy is the primary 
  (step 4) to test the performance of the new pool. If the performance is acceptable, the volume 
  copy in tier 1 can be split or deleted. If the testing of the tier 2 pool shows unsatisfactory 
  performance, the old copy can be made the primary again to switch volume reads back to the 
  tier 1 copy. 