text: **11.6.5 Metro Mirror overview**
  
  Metro Mirror establishes a synchronous relationship between two volumes of equal size. The 
  volumes in a Metro Mirror relationship are referred to as the master (primary) volume and the 
  auxiliary (secondary) volume. Traditional FC Metro Mirror is primarily used in a metropolitan 
  area or geographical area, up to a maximum distance of 300 km (186.4 miles) to provide 
  synchronous replication of data. 
  
  With synchronous copies, host applications write to the master volume, but they do not 
  receive confirmation that the write operation completed until the data is written to the auxiliary 
  volume. This action ensures that both the volumes have identical data when the copy 
  completes. After the initial copy completes, the Metro Mirror function always maintains a fully 
  synchronized copy of the source data at the target site. 
  
  Metro Mirror has the following characteristics: 
  
  (cid:2) Zero recovery point objective (RPO) 
  (cid:2) Synchronous 
  (cid:2) Production application performance that is affected by round-trip latency 
  
  Increased distance directly affects host I/O performance because the writes are synchronous. 
  Use the requirements for application performance when you are selecting your Metro Mirror 
  auxiliary location. 
  
  Consistency groups can be used to maintain data integrity for dependent writes, which is 
  similar to FlashCopy Consistency Groups. 