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Expand Configuration and Management Manual (G06.24+)

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Expand Overview
Expand Configuration and Management Manual—523347-008
2-7
ServerNet Clusters
ServerNet Clusters
ServerNet Clusters use Expand to provide a high-speed interconnect between servers
over a limited geographic range. Three network topologies are supported: the star,
split-star, and tri-star topologies. The star topology supports up to eight nodes. The
split-star topology supports up to 16 nodes. The tri-star topology supports up to 24
nodes
The 16-node configuration is split between two NonStop cluster switches per external
fabric in what is known as a split-star topology and the 24-node configuration is split
between three cluster switches per external fabric in what is known as a tri-star
topology. Using single-mode fiber-optic cables to link the two centers of the split-star
and the three centers of the tri-star allows a greater distance (up to 1 kilometer)
between the cluster switches and their connected nodes.
For detailed topology information, see Section 4, Planning for ServerNet Clusters.
A NonStop S-series server cannot participate in more than one ServerNet cluster.
Distributed Control
The control function of the Expand subsystem is distributed throughout the network.
Unlike a hierarchical network, in which a central computer, or host, controls the
communications environment, nodes in an Expand network communicate with each
other as peers. Distributed networks have the following additional advantages:
•
Distributed applications. Applications can be distributed so that multiple nodes
share the processing load.
•
Flexible network topologies. The network topology can be designed without regard
to host or controlling processors.
•
Network reliability. Failure of one node does not necessarily affect the operation of
other nodes in the network.
Automatic Message Routing
The Expand subsystem’s routing facilities ensure that a message sent from any node
in the network will arrive at its destination as long as there is at least one active
communications path available. The Expand subsystem’s routing capabilities also
include the following:
•
Passthrough Routing
•
Best-Path Routing
•
Priority Routing
Refer to Time Factors and Pathchange Messages on page 18-24 for information on
adjusting settings so that routing is optimal.