text: **7.4 HyperSwap volumes**
  
  The HyperSwap function provides highly available volumes accessible through two sites at up 
  to 300 km (186.4 miles) apart. A fully independent copy of the data is maintained at each site. 
  
  When data is written by hosts at either site, both copies are synchronously updated before the 
  write operation completion is reported to the host. The HyperSwap function automatically 
  optimizes itself to minimize data transmitted between sites and to minimize host read and 
  write latency. 
  
  If the nodes or storage at either site go offline, the HyperSwap function automatically fails 
  over access to the other copy. The HyperSwap function also automatically resynchronizes the 
  two copies when possible. 
  
  The HyperSwap function is built on the foundation of two earlier technologies: Non-Disruptive 
  Volume Move (NDVM) function that was introduced in IBM Spectrum Virtualize V6.4, and the 
  Remote Copy features that include Metro Mirror, Global Mirror, and Global Mirror with Change 
  Volumes. 