NonStop Systems Introduction

NonStop Server Architecture
NonStop Systems Introduction—527825-001
7-10
ServerNet Clustering for Availability and
Performance
However, if a word of main memory gets an uncorrectable error, the operating system
immediately halts the processor. The remaining processors notice the absence of “I’m
alive” messages, declare the processor to be down, and take over for the down
processor.
ServerNet Clustering for Availability and
Performance
You have seen how the processors of a NonStop server communicate with each other
over dual ServerNet fabrics. The fabrics provide a fast, efficient, and reliable way for
the processors to exchange messages.
ServerNet technology can also be used to connect servers in groups called ServerNet
clusters. ServerNet clusters extend the ServerNet X and Y fabrics outside the system
boundary and allow ServerNet to be used for messaging between systems. A
ServerNet cluster consists of individual servers, each containing internal X and Y
fabrics, connected through fiber-optic cables and NonStop cluster switches to other
servers. The fiber-optic cables and NonStop cluster switches constitute external
ServerNet X and Y fabrics. Figure 7-7 on page 7-10 shows how a ServerNet cluster
extends the X and Y fabrics to multiple systems.
Figure 7-7. 4-Node ServerNet Cluster
Node 1 Node 2 Node 4
ServerNet
interface
Node 3
XYY X X YY X
External ServerNet Y fabric
External ServerNet X fabric
ServerNet
interface
ServerNet
interface
ServerNet
interface
VST096.vsd
Cluster switch
Cluster switch