text: Global Mirror write I/O from production system to a secondary system requires serialization 
  and sequence-tagging before being sent across the network to a remote site (to maintain a 
  write-order consistent copy of data). 
  
  To avoid affecting the production site, IBM Spectrum Virtualize supports more parallelism in 
  processing and managing Global Mirror writes on the secondary system by using the 
  following methods: 
  
  (cid:2) Secondary system nodes store replication writes in new redundant non-volatile cache 
  (cid:2) Cache content details are shared between nodes 
  (cid:2) Cache content details are batched together to make node-to-node latency less of an issue 
  (cid:2) Nodes intelligently apply these batches in parallel as soon as possible 
  (cid:2) Nodes internally manage and optimize Global Mirror secondary write I/O processing 
  
  In a failover scenario where the secondary site must become the master source of data, 
  certain updates might be missing at the secondary site. Therefore, any applications that use 
  this data must have an external mechanism for recovering the missing updates and 
  reapplying them, such as a transaction log replay. 
  
  Global Mirror is supported over FC, FC over IP (FCIP), FC over Ethernet (FCoE), and native 
  IP connections. The maximum distance cannot exceed 80 ms round trip, which is about 
  4000 km (2485.48 miles) between mirrored systems. However, starting with IBM Spectrum 
  Virtualize V7.4, this distance was significantly increased for certain IBM Storwize Gen2 and 
  IBM SAN Volume Controller configurations. Figure 11-90 shows the current supported 
  distances for Global Mirror remote copy. 