text: (cid:2) IBM Spectrum Virtualize does not require a control network or fabric to be installed to 
  
  manage Global Mirror. For intercluster Global Mirror, the system maintains a control link 
  between the two systems. This control link is used to control the state and to coordinate 
  the updates at either end. The control link is implemented on top of the same FC fabric 
  connection that the system uses for Global Mirror I/O. 
  
  (cid:2) IBM Spectrum Virtualize implements a configuration model that maintains the Global 
  Mirror configuration and state through major events, such as failover, recovery, and 
  resynchronization, to minimize user configuration action through these events. 
  
  (cid:2) IBM Spectrum Virtualize implements flexible resynchronization support, enabling it to 
  
  resynchronize volume pairs that experienced write I/Os to both disks, and to 
  resynchronize only those regions that changed. 
  
  (cid:2) An optional feature for Global Mirror is a delay simulation to be applied on writes that are 
  sent to auxiliary volumes. It is useful in intracluster scenarios for testing purposes. 
  
  **Colliding writes**
  The Global Mirror algorithm requires that only a single write is active on a volume. I/Os that 
  overlap an active IO are sequential, which is called*colliding writes.*If another write is 
  received from a host while the auxiliary write is still active, the new host write is delayed until 
  the auxiliary write is complete. This rule is needed if a series of writes to the auxiliary must be 
  tried again, which is called*reconstruction*. Conceptually, the data for reconstruction comes 
  from the master volume. 