Designing Disaster Tolerant High Availability Clusters, 10th Edition, March 2003 (B7660-90013)

Building a Metropolitan Cluster Using MetroCluster/SRDF
Setting up M by N Configurations
Chapter 4 159
Figure 4-19 shows a 2 by 2 configuration. Data in this figure are used in
the example commands given in the following sections. The example
shows R1 devices at one data center and R2 devices with Business
Continuity Volumes (BCVs) at the other, but a bidirectional
configuration is also possible, with R1 devices on both sites.
Figure 4-19 Devices and Symmetrix Units in M by N Configurations
Creating Symmetrix Device Groups
For each node on the R1 side (node1 and node2), create the device groups
as follows. You have to create two device groups because device groups do
not span frames.
NOTE In a 1 by 2 or 2 by 1 configuration, on either the R1 or R2 side, whichever
side has the one Symmetrix frame, a minimum of two device groups is
required. The rule of thumb is that you need one device group per RDF
group (RA group), even if you have only one frame on that side.