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

Cascading Failover in a Continental Cluster
Overview
Chapter 8 365
played by either Symmetrix in the primary cluster. In Figure 8-1,
Symm1 holds the R1 volumes for application X data, and Site 1 is known
as the primary site for application X. Symm2 holds R1 volumes for
application Y data, and Site 2 is the primary site for application Y.
The recovery Symmetrix holds a remote replicated copy of the data in
the recovery cluster. The data center that houses the recovery
Symmetrix is called the recovery site. In Figure 8-1, Symm3 is the
recovery Symmetrix for both application X data and application Y data,
and Site 4 is the recovery site for both application X and application Y.
Symmetrix Configuration
There are three EMC Symmetrix disk arrays. Each has a minimum of
two 2-port RDF Director boards. The basic configuration requires the
following in both Symmetrixes in the primary cluster:
• R1 volumes in the primary Symmetrix to hold the primary data for
an application
• R2 volumes in the secondary Symmetrix to hold a current copy of the
data for an application
• Business Continuity volumes (BCV’s) in the secondary Symmetrix to
be used as the intermediary volumes to replicate the data to the
recovery Symmetrix
• R2 volumes in the recovery Symmetrix to hold a point in time copy of
the data
• BCV’s in the recovery Symmetrix to protect the data from corruption
due to rolling disaster
• Two ESCON connections over WAN using ESCON converters
between the secondary Symmetrix and the recovery Symmetrix
• Two direct ESCON connections (ESCON extenders are needed if the
distance is over 3 kilometers) between the primary Symmetrix and
the secondary Symmetrix