Cascading Failover in a Continentalclusters, December 2005

Figure 1 - Replication Setup
Also, the figure shows at a high level how the data replication is connected. In the primary cluster, the
primary replication group has two devices: a source device (connected to the primary site labeled as
device A) and a destination (connected to the secondary site and labeled as device B). Data is
replicated via storage data replication facilities (e.g. Continuous Access) continuously from source to
destination. On the secondary site, a local mirror is associated with the destination devices (labeled
as device B’). The mirror technology is storage specific (e.g. Business Copy). This local mirror also
acts as a source device for the recovery replication group and recovery during rolling disasters. In the
recovery cluster, the destination device (labeled as device C) of the recovery replication group are
connected to the nodes in the cluster. Data is periodically replicated to the destination devices via
storage data replication technology. Also, a local mirror of the destination device is required for
cases of rolling disasters (labeled as device C’).
Currently, HP StorageWorks XP Continuous Access (CA) and EMC Symmetrix SRDF technologies are
supported for the multi-site disaster tolerant solution.
Purpose
This document introduces the cascaded configuration in a Continentalclusters environment. This
includes configuration, maintenance, and recovery procedure for the cascaded configuration
environment.
Terminology
Throughout this document, the following terms refer to high level operations performed under a
cascaded configuration scenario. These defined terms are not general terms that are used in other
documents referring to data replication, clustering, and multi-site disaster tolerant solutions.
The device where I/O can be performed is referred to as the source. The data that is written to the
source device will be replicated to another device remotely. This remote device is referred to as the
destination (or destination device). For the XP CA data replication technology, the correct terminology
for source and destination are PVOL and SVOL respectively. For the EMC SRDF data replication
technology, source and destination are R1 and R2 respectively. Local mirror is the name for a local
copy of a device on the same disk array. Business Copy (BC) for HP XP and Business Continuance
Volumes (BCV) for EMC SRDF are the supported local mirroring capabilities used for the Metrocluster
and Continentalclusters products. A replication group is a pairing of source and destination devices
where the source replicates data to its assigned destination. In the cascaded configuration, there are
two replication groups. The replication group in the primary cluster is referred to as the primary
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