NonStop S-Series Server Description Manual (G06.24+)

Introduction
HP NonStop S-Series Server Description Manual—520331-003
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Tr i-Star Top ology
Tri-Star Topology
The tri-star topology, introduced with the G06.14 RVU, supports up to 24 nodes and is
required for clusters using 6770 switches that have more than 16 nodes.
Figure 1-23 shows both fabrics of a 24-node ServerNet cluster connected in a tri-star
topology.
The tri-star topology uses up to six cluster switches—three for the X fabric (referred to
as X1, X2 and X3) and three for the Y fabric (referred to as Y1, Y2, and Y3).
The first cluster switch on a fabric (X1 or Y1) supports ServerNet nodes 1 through 8,
the second cluster switch on the same fabric (X2 or Y2) supports ServerNet nodes 9
through 16, and the third cluster switch on the same fabric (X3 or Y3) supports
ServerNet nodes 17 through 24.
In the tri-star topology, the three cluster switches on each fabric are connected by three
two-lane links, each consisting of two fiber-optic cables. Ports 8 through 11 of the
cluster switches are used for the two-lane links. Traffic travels in both directions across
both lanes of the links.
The tri-star topology features automatic fail-over of ServerNet traffic on the two-lane
links. As long as at least one link is operational between cluster switches, processor
paths between ServerNet nodes can remain up on both fabrics.