text: The*grains per second*numbers represent the maximum number of grains that the Storwize 
  V7000 copies per second. This amount assumes that the bandwidth to the managed disks 
  (MDisks) can accommodate this rate. 
  
  If the Storwize V7000 cannot achieve these copy rates because of insufficient width from the 
  nodes to the MDisks, the background copy I/O contends for resources on an equal basis with 
  the I/O that is arriving from the hosts. Background copy I/O and I/O that is arriving from the 
  hosts tend to see an increase in latency and a consequential reduction in throughput. 
  
  Background copy and foreground I/O continue to progress, and do not stop, hang, or cause 
  the node to fail. 
  
  The background copy is performed by one of the nodes that belong to the I/O group in which 
  the source volume resides. This responsibility is moved to the other node in the I/O group if 
  the node that performs the background and stopping copy fails. 