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

Figure 1 High Availability Architecture.
node 1 node 2
pkg A
pkg B
pkg A mirrors
pkg B mirrors
pkg B disks
pkg A disks
Client Connections
X
pkg A fails
over to node 2
node 1 node 2
pkg B
pkg A mirrors
pkg B mirrors
pkg B disks
pkg A disks
Client Connections
X
pkg A
node 1 fails
This architecture, which is typically implemented on one site in a single data center, is sometimes
called a local cluster. For some installations, the level of protection given by a local cluster is
insufficient. Consider the order processing center where power outages are common during harsh
weather. Or consider the systems running the stock market, where multiple system failures, for any
reason, have a significant financial impact. For these types of installations, and many more like
them, it is important to guard not only against single points of failure, but against multiple points
of failure (MPOF), or against single massive failures that cause many components to fail, such as
the failure of a data center, of an entire site, or of a small area. A data center, in the context of
disaster recovery, is a physically proximate collection of nodes and disks, usually all in one room.
Creating clusters that are resistant to multiple points of failure or single massive failures requires a
different type of cluster architecture called a disaster recovery architecture.This architecture provides
you with the ability to fail over automatically to another part of the cluster or manually to a different
cluster after certain disasters. Specifically, the disaster recovery cluster provides appropriate failover
in the case where a disaster causes an entire data center to fail, as in Figure 2.
10 Disaster Recovery in a Serviceguard Cluster