text: If you stop the Source-T1 mapping while Source-T0 mapping and Source-T2 are still in 
  copying mode, the grains that are not yet copied on T0 are copied from T1 to T0 (next oldest). 
  T0 now depends upon T2. 
  
  Your target volume is still accessible while the cleaning process is running. When the system 
  is operating in this mode, it is possible that host I/O operations can prevent the cleaning 
  process from reaching 100% if the I/O operations continue to copy new data to the target 
  volumes. 