Understanding and Designing Serviceguard Disaster Recovery Architectures

Cascading Failover Using Metrocluster
This configuration uses three data replication groups, two of which are part of the Metrocluster
and the other attached to the recovery cluster. The data centers are distributed as follows:
• Primary—on the site that holds the primary copy of the data, located in the primary cluster.
• Secondary—on the site that holds a remote mirror copy of the data, located in the primary
cluster.
• Arbitrator or Quorum Server—a third location that contains the arbitrator nodes, or quorum
server located in the primary cluster.
• Recovery—on a site that holds a remote mirror copy of the data, located in the recovery
cluster.
Figure 14 illustrates data centers, clusters, and nodes in a cascading failover configuration, and
shows at a high level how the data replication is connected. The primary cluster consists of two
storage devices: a source device (connected to the primary site and labeled as device A) and a
destination device (connected to the secondary site and labeled as device B). Data is replicated
via storage data replication facilities (for example, Continuous Access) continuously from source
to destination.
On site 2, a local mirror is associated with the destination devices (labeled as device B’). The
mirror technology is storage specific (for example, Business Copy). This local mirror also acts as
a source device for recovery during rolling disasters.
A rolling disaster is defined as a disaster that occurs before the cluster is able to recover from a
non-disastrous failure. An example is a data replication link that fails, and when it is being restored
and data is being resynchronized, a disaster causes an entire data center to fail.
In the recovery cluster, on site 4, the destination device (labeled as device C) is connected to the
node in the cluster. Data is periodically replicated to the destination devices via storage data
replication technology. A local mirror of the destination device is required on site 4 for cases of
rolling disasters (labeled as device C’). Currently, HP Storage XP or P9000 Continuous Access
and EMC Symmetrix SRDF technologies are supported for the multi-site disaster recovery solution.
32 Metrocluster and Continentalclusters