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Building an Extended Distance Cluster Using Serviceguard and Software RAID
Rules for Separate Network and Data Links
Chapter 2 57
Rules for Separate Network and Data Links
• 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.
• There can be a maximum of 500 meters between the Fibre Channel
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 switches. If DWDM links are used, the
maximum distance between the data centers is 100 kilometers. For
more information on link technologies, see Table 2-1 on page 52.
• 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.
• There must be at least two alternately routed Fibre Channel Data
Replication links between each data center.
• See the HP Configuration Guide (available through your HP
representative) for a list of supported Fibre Channel hardware.