HP Serviceguard Extended Distance Cluster for Linux A.12.00.00 Deployment Guide, March 2014

• 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 recommended over Fibre Channel hubs.
• For disaster recovery, application data must be mirrored between the primary data centers.
You must ensure that the mirror copies reside in different data centers, as the software cannot
determine the locations.
NOTE: When a failure results in the mirror copies losing synchronization, MD will perform
a full resynchronization when both halves of the mirror are available.
2.4 Guidelines for Separate Network and Data Links
• There must be less than 200 milliseconds of latency in the network 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 “Link Technologies and Distances” (page 17).
• 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.
2.5 Guidelines on DWDM Links for Network and Data
• 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 supported between the data centers for DWDM configurations is 100
kilometers.
• Both the networking and Fibre Channel Data Replication can go through the same DWDM
box - separate DWDM boxes are not required.
• Since DWDM converters are typically designed to be fault tolerant, it is acceptable to use
only one DWDM box (in each data center) for the links between each data center. However,
for the highest availability, it is recommended to use two separate DWDM boxes (in each
data center) for the links between each data center. If using a single DWDM box for the links
between each data center the redundant standby fibre link feature of the DWDM box must
18 Building an Extended Distance Cluster Using Serviceguard and Software RAID