Understanding and Designing Serviceguard Disaster Tolerant Architectures Fourth Edition, December 2007 (T1906-90023)

Building an Extended Distance Cluster Using Serviceguard
Rules for Separate Network and Data Links
Chapter 290
Rules for Separate Network and Data Links
• The network interfaces used must support DLPI (link level).
• There must be less than 200 milliseconds of latency in the network
between the data centers.
• No routing is allowed for the networks between the data centers.
• Routing is allowed to the third data center if a Quorum Server is
used in that data center.
• The maximum distance between the data centers for this type of
configuration is currently limited by the maximum distance
supported for the networking type or Fibre Channel link type being
used, whichever is shorter.
• Currently, FDDI offers a total ring length of 100 kilometers. This
will allow up to 50 kilometers between data centers for both two and
three data center solutions.
• There can be a maximum of 500 meters between the Fibre Channel
hubs or switches in the two data centers if Short-wave ports are
used. This distance can be increased to 10 kilometers by using a
Long-wave Fibre Channel port on the hubs or switches. The distance
can be increased to 80 kilometers if Finisar (Long-haul) GBICs are
used in Fibre Channel switches (hubs are not supported for this
distance). If DWDM links are used, the maximum distance between
the data centers is 100 kilometers.
• There must be at least two alternately routed networking links
between each primary data center to prevent the “backhoe problem”.
The “backhoe problem” can occur when all cables are routed through
a single trench and a tractor on a construction job severs all cables
and disables all communications between the data centers. It is
allowable to have only a single network link routed from each
primary data center to the third location, however in order to survive
the loss of the network link between a primary data center and the
arbitrator data center, the network routing should be configured so
that a primary data center can also reach the arbitrator via a route
which passes through the other primary data center.