ServerNet Cluster 6780 Planning and Installation Guide (G06.28+, H06.05+)

Table Of Contents
ServerNet Cluster Overview
ServerNet Cluster 6780 Planning and Installation Guide527301-005
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ServerNet Clusters
ServerNet Clusters
ServerNet clusters allow multiple multiprocessor nodes to work together and appear to
client applications as one large processing entity. This interconnection technology uses
the ServerNet protocol to pass information from one node to any other node in the
cluster.
ServerNet Fabrics
A fabric is a collection of connected routers and ServerNet links. Two identically
configured fabrics, the X fabric and the Y fabric, together provide a fault-tolerant
interconnection for NonStop S-series servers. ServerNet clusters extend the ServerNet
X and Y fabrics outside the system boundary and allow the ServerNet protocol to be
used for intersystem messaging.
Communication occurs on both fabrics simultaneously for increased throughput. Each
processor connects to both fabrics. The X fabric and the Y fabric are not connected to
each other. Therefore, a ServerNet packet cannot cross from one fabric to the other,
and a failure in one fabric does not affect the other fabric. This fault tolerance at the
hardware level enhances availability.
Internal ServerNet Fabrics
Each node in a ServerNet cluster contains two identical internal ServerNet fabrics (X
and Y). An internal ServerNet X or Y fabric delivers ServerNet packets between
ServerNet end devices within a NonStop S-series server.
External ServerNet Fabrics
External fabrics provide communication between nodes. The external ServerNet
fabrics are an extension of the internal ServerNet fabrics beyond the single-system
boundary. An external ServerNet X or Y fabric delivers ServerNet packets between
ServerNet nodes.
The nodes in a ServerNet cluster are connected to each other through fiber-optic
cables and cluster switches. The external ServerNet X and Y fabrics consists of the
cables, the cluster switches, and the connection to the NonStop server.
Every ServerNet cluster has identical, external X and Y fabrics. The loss of one node
does not affect the other nodes in the cluster.
Note. For ServerNet clusters, a 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.