NonStop Systems Introduction

NonStop Server Architecture
NonStop Systems Introduction—527825-001
7-4
Interconnected Multiple Processors
the other disk. For more information on mirrored disks, see Mirrored Disk Volumes on
page 7-8.
The following discussions take a closer look at the structure of the ServerNet fabrics
and the ways that they ensure the continuous availability of processes and databases.
Interconnected Multiple Processors
A NonStop system consists of 2 to 16 processors. Figure 7-4 on page 7-4 shows a
simple four-processor configuration. (For now, I/O is omitted.) Each processor in this
system is an autonomous computer in its own right, each having its own memory and
operating system software. The ServerNet fabrics make it possible for all the
processors in the system to communicate with each other and to cooperate in
executing applications. Each processor is a ServerNet node, in this architecture, and
each has a ServerNet node ID.
Notice that the two fabrics are identified as the X fabric and the Y fabric, and that no
router connects to both the X fabric and the Y fabric. Also notice that each processor
connects to a single router in each fabric. For example, Processor 0 connects to router
5 in the X fabric and to router 1 in the Y fabric.
The use of two fabrics ensures that two paths exist between all the processors in the
system. If a path through one fabric fails, there is always another path through the
other fabric. Thus, in conjunction with the file system and message system, the
Figure 7-4. Dual Data Paths Between Processors
Processor 0 Processor 1 Processor 3
ServerNet
interface
3 41 2
8765
Processor 2
XYY X X YY X
ServerNet Y fabric
ServerNet X fabric
ServerNet
interface
ServerNet
interface
ServerNet
interface
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