text: Various operating systems and applications provide facilities to stop I/O operations and 
  ensure that all data is flushed from host cache. If these facilities are available, they can be 
  used to prepare for a FlashCopy operation. When this type of facility is unavailable, the host 
  cache must be flushed manually by quiescing the application and unmounting the file system 
  or drives. 
  
  The target volumes are overwritten with a complete image of the source volumes. Before the 
  FlashCopy mappings are started, any data that is held on the host operating system (or 
  application) caches for the target volumes must be discarded. The easiest way to ensure that 
  no data is held in these caches is to unmount the target volumes before the FlashCopy 
  operation starts. 
  
  **Preferred practice:**From a practical standpoint, when you have an application that is 
  backed by a database and you want to make a FlashCopy of that application’s data, it is 
  sufficient in most cases to use the write-suspend method that is available in most modern 
  databases. This is possible because the database maintains strict control over I/O. 
  
  This method is as opposed to flushing data from both the application and the backing 
  database, which is always the suggested method because it is safer. However, this method 
  can be used when facilities do not exist or your environment includes time sensitivity. 