NonStop S-Series Server Description Manual (G06.27+)

Introduction

HP NonStop S-Series Server Description Manual—520331-004

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Cluster Topologies for 6770 Switches

ServerNet clusters that use 6770 switches can have one of three topologies: star, split-

star, and tri-star. Figure 1-22, which illustrates only one fabric for simplicity, shows the

basic concept of all three of these topologies. Each has its own maximum number of

servers that can exist in a cluster: 8, 16, or 24, respectively.

As you look over Figure 1-22, keep in mind that each server icon shown as a

component of a cluster is actually a full Tetra 16 multiprocessor server, such as the

maximum example shown previously in Figure 1-19 on page 1-37. Each such server,

when connected in a cluster, is a ServerNet node.

All the servers in a cluster are connected to all other servers in that cluster through

fiber-optic cables and cluster switches. The cables and cluster switches constitute the

external ServerNet X and Y fabrics. This term differentiates these fabrics from

fabrics that are contained within a single server, which can be termed the internal

ServerNet X and Y fabrics.

In all three topologies, each node has two independent connections (the X and Y

fabrics) to two independent cluster switches. The loss of a node does not affect the

other nodes in the cluster.

You can build your cluster as a subset of either the split-star or the tri-star topology.

For example, even though a tri-star topology can contain three cluster switches for

each fabric, you can build a tri-star topology that uses only one or two switches for

each fabric. By building a subset of a topology, you are positioned to grow the cluster

quickly online as your applications grow.

ServerNet clustering is compatible with all other products based on the Expand

product. For example, a node in a FOX ring can simultaneously function as a node in a

ServerNet cluster. Nodes in a ServerNet cluster can also coexist as systems belonging

to an Expand network; in that case, each server is both an Expand node and a

ServerNet node. ServerNet clusters can also coexist with ATM, Ethernet, Fast

Ethernet, Token Ring, and other WAN and LAN products.

Note. A ServerNet cluster is a collection of servers, or nodes, that can function either

independently or collectively as a processing unit. This use of cluster differs from the definition

of a cluster in a FOX ring. In a FOX ring, a cluster is synonymous with server and refers to a

collection of processors and I/O devices rather than a collection of servers.