HP Serviceguard Extended Distance Cluster for Linux A.11.20.10 Deployment Guide, December 2012

Figure 2 Disaster Recovery Architecture
1.3 Understanding Types of Disaster Recovery Clusters
To protect against multiple points of failure, cluster components must be geographically dispersed:
nodes can be put in different rooms, on different floors of a building, or even in separate buildings
or separate cities. The distance between the nodes is dependent on the types of disaster from which
you need protection, and on the technology used to replicate data. Three types of disaster-recovery
clusters are described in this guide:
• Extended Distance Clusters
• Metrocluster
• Continental Cluster
These types differ from a simple local cluster in many ways. Extended distance clusters and
metropolitan clusters often require right-of-way from local governments or utilities to lay network
and data replication cables or connect to DWDMs. This can complicate the design and
implementation. They also require a different kind of control mechanism for ensuring that data
integrity issues do not arise, such as a quorum server. Typically, extended distance and metropolitan
clusters use an arbitrator site containing a computer running a “quorum” application. Continental
clusters span great distances and operate by replicating data between two completely separate
local clusters.
1.3.1 Extended Distance Clusters
An extended distance cluster (also known as extended campus cluster) is a normal Serviceguard
cluster that has alternate nodes located in different data centers separated by some distance, with
a third location supporting the quorum service. Extended distance clusters are connected using a
high speed cable that guarantees network access between the nodes as long as all guidelines for
disaster recovery architecture are followed. Extended distance clusters were formerly known as
campus clusters, but that term is not always appropriate because the supported distances have
increased beyond the typical size of a single corporate campus. The maximum distance between
1.3 Understanding Types of Disaster Recovery Clusters 11