text: (cid:2) Cleaning rate: No 
  (cid:2) Primary copy source pool: Target pool 
  
  **Use case**
  The user wants to produce a copy of a volume without affecting the availability of the volume. 
  The user does not anticipate many changes to be made to the source or target volume; a 
  significant proportion of the volumes remains unchanged. 
  
  By ensuring that only changes require a copy of data to be made, the total amount of disk 
  space that is required for the copy is reduced. Therefore, many Snapshot copies can be used 
  in the environment. 
  
  Snapshots are useful for providing protection against corruption or similar issues with the 
  validity of the data, but they do not provide protection from physical controller failures. 
  Snapshots can also provide a vehicle for performing repeatable testing (including “what-if” 
  modeling that is based on production data) without requiring a full copy of the data to be 
  provisioned. 
  
  For example, in Figure 11-16, the source volume user can still work on the original data 
  volume (such as a production volume) and the target volumes can be accessed instantly. 
  Users of target volumes can modify the content and perform “what-if” tests for example 
  (versioning). Storage administrators do not need to perform full copies of a volume for 
  temporary tests. However, the target volumes need to remain linked to the source. Whenever 
  the link is broken (FlashCopy mapping stopped or deleted), the target volumes become 
  unusable. 