HP Serviceguard Extended Distance Cluster for Linux A.01.00 Deployment Guide, Second Edition, May 2008

Disaster Tolerance and Recovery in a Serviceguard Cluster
Understanding Types of Disaster Tolerant Clusters
Chapter 120
Figure 1-3 Extended Distance Cluster
In the above configuration the network and FC links between the data
centers are combined and sent over common DWDM links. Two DWDM
links provide redundancy. When one of them fails, the other may still be
active and may keep the two data centers connected. Using the DWDM
link, clusters can now be extended to greater distances which were not
possible earlier due to limits imposed by the Fibre Channel link for
storage and Ethernet for networks. Storage in both data centers is
connected to both the nodes via two FC switches in order to provide
multiple paths. This configuration supports a distance up to 100 kms
between datacenter1 and datacenter2.