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

Building an Extended Distance Cluster Using MC/ServiceGuard
Two Data Centers and Third Location Architectures
Chapter 258
Two Data Centers and Third Location
Architectures
Configurations with two data centers and third location have the
following requirements:
• In these solutions, there must be an equal number of nodes (1-7) or
(1-8 if a Quorum Server is used) in each primary data center, and the
third location (known as the arbitrator data center) or Quorum
Server can contain 1 or 2 nodes. Cluster lock disks must not be
configured.
• The abritrator nodes are standard MC/ServiceGuard nodes
configured in the cluster; however, they are not allowed to be
connected to the shared disks in either of the primary data centers.
Arbitrator nodes are used as tie-breakers to maintain cluster
quorum when all communication between the two primary data
centers is lost. The third location containing the arbitrator nodes
must be located separately from the primary data centers.
It is possible to use a single MC/ServiceGuard Quorum Server node
in place of Arbitrator node(s); however, the quorum server system
must still be located in third location separate from the primary data
centers. For more information about quorum server, refer to the
manual Managing MC/ServiceGuard and to the MC/ServiceGuard
Quorum Server Release Notes.
• If ServiceGuard OPS Edition is used, then there can only be two
nodes configured to share OPS data, as MirrorDisk/UX only supports
concurrent volume group activation for up to two nodes. CVM allows
for clusters containing 2 or 4 nodes.
• 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. See below, “Network and
Data Replication Between the Data Centers” for more detail.
• Fibre Channel Direct Fabric Attach (DFA) is recommended over
Fibre Channel Arbitrated loop configurations, due to the superior
performance of DFA, especially as the distance increases. Therefore
Fibre Channel switches are preferred over Fibre Channel hubs.