HP Serviceguard Extended Distance Cluster for Linux A.01.01 Deployment Guide, Third Edition, May 2008

Building an Extended Distance Cluster Using Serviceguard and Software RAID
Two Data Center and Quorum Service Location Architectures
Chapter 2 51
Two Data Center and Quorum Service
Location Architectures
A two data center and Quorum Service location, which is at a third
location, have the following configuration requirements:
NOTE There is no hard requirement on how far the Quorum Service location
has to be from the two main data centers. It can be as close as the room
next door with its own power source or can be as far as in another site
across town. The distance between all three locations dictates that level
of disaster tolerance a cluster can provide.
• In these solutions, there must be an equal number of nodes in each
primary data center, and the third location (known as the arbitrator
data center) contains the Quorum Server. LockLUN is not supported
in a Disaster Tolerant configuration. In this release, only one node in
each data center is supported.
• The Quorum Server is used as a tie-breaker to maintain cluster
quorum when all communication between the two primary data
centers is lost. The arbitrator data center must be located separately
from the primary data centers. For more information about quorum
server, see the Managing Serviceguard user’s guide and the
Serviceguard Quorum Server Release Notes.
• A minimum of two heartbeat paths must be configured for all cluster
nodes. The preferred solution is two separate heartbeat subnets
configured in the cluster, each going over a separately routed
network path to the other data center. Alternatively, there can be a
single dedicated heartbeat subnet with a bonded pair configured for
it. Each would go over a separately routed physical network path to
the other data centers.
• There can be separate networking and Fibre Channel links between
the data centers, or both networking and Fibre Channel can go over
DWDM links between the data centers.