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

Disaster Tolerance and Recovery in an MC/ServiceGuard Cluster
Types of Disaster Tolerant Clusters
Chapter 122
Types of Disaster Tolerant 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-tolerant clusters are described in
this guide:
• Extended Distance Clusters
• Metropolitan Clusters
• Continental Clusters
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
cable. 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. Typically, metropolitan clusters use an
arbitrator site containing additional cluster nodes instead of the cluster
lock disk. Continental clusters span great distances and operate by
replicating data between two completely separate local clusters.
Extended Distance Clusters
An extended distance cluster (also known as extended campus
cluster) has alternate nodes located in different data centers separated
by some distance. Extended distance clusters are connected using a high
speed cable that guarantees network access between the nodes as long as
all guidelines for disaster tolerant 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