text: **11.11.2 1720 error**
  
  The 1720 error (event ID 050020) is the other problem remote copy might encounter. The 
  amount of bandwidth that is needed for system-to-system communications varies based on 
  the number of nodes. It is important that it is not zero. When a partner on either side stops 
  communication, a 1720 is displayed in your error log. According to the product documentation, 
  there are no likely field-replaceable unit breakages or other causes. 
  
  The source of this error is most often a fabric problem or a problem in the network path 
  between your partners. When you receive this error, check your fabric configuration for zoning 
  of more than one host bus adapter (HBA) port for each node per I/O Group if your fabric has 
  more than 64 HBA ports zoned. The suggested zoning configuration for fabrics is one port for 
  each node per I/O Group per fabric that is associated with the host. 
  
  For those fabrics with 64 or more host ports, this suggestion becomes a rule. Therefore, you 
  see four paths to each volume discovered on the host because each host needs to have at 
  least two FC ports from separate HBA cards, each in a separate fabric. On each fabric, each 
  host FC port is zoned to two IBM SAN Volume Controller node ports where each node port 
  comes from a different IBM SAN Volume Controller node. This configuration provides four 
  paths per volume. More than four paths per volume are supported but not recommended. 