text: **11.6.14 Distribution of work among nodes**
  
  For the best performance, MM/GM volumes must have their preferred nodes evenly 
  distributed among the nodes of the systems. Each volume within an I/O Group has a 
  preferred node property that can be used to balance the I/O load between nodes in that 
  group. MM/GM also uses this property to route I/O between systems. 
  
  If this preferred practice is not maintained, such as if source volumes are assigned to only 
  one node in the I/O group, you can change the preferred node for each volume to distribute 
  volumes evenly between the nodes. You can also change the preferred node for volumes that 
  are in a remote copy relationship without affecting the host I/O to a particular volume. 
  
  The remote copy relationship type does not matter. The remote copy relationship type can be 
  Metro Mirror, Global Mirror, or Global Mirror with Change Volumes. You can change the 
  preferred node both to the source and target volumes that are participating in the remote copy 
  relationship. 
  
  **11.6.15 Background copy performance**
  
  The background copy performance is subject to sufficient RAID controller bandwidth. 
  Performance is also subject to other potential bottlenecks, such as the intercluster fabric, and 
  possible contention from host I/O for the IBM Spectrum Virtualize system bandwidth 
  resources. 