NonStop NS-Series Operations Guide (H06.12+)

A processor with two NonStop Blade Elements comprise the dual modular redundant (DMR)
NonStop Blade Complex, which is also referred to as a duplex system. This duplex system
provides data integrity and system availability that is comparable to NonStop S-series systems,
but at considerably faster processing speeds.
Three NonStop Blade Elements plus their associated LSUs make up the triple modular redundant
(TMR) NonStop Blade Complex, which is referred to as a triplex system. The triplex system
provides the same processing speeds as the duplex system while also enabling hardware fault
recovery that is transparent to all but the lowest level of the NonStop operating system (OS).
In the event of a processor fault in either a duplex or triplex system, the failed component within
a NonStop Blade Element (processor element, power supply, and so forth) can be replaced while
the system continues to run. A single Integrity NonStop system can have up to four NonStop
Blade Complexes for a total of 16 processors. Processors communicate with each other and with
the system I/O over dual ServerNet fabrics.
A ServerNet fabric is a complex web of links that provide a large number of possible paths from
one point to another. Two communications fabrics, the X and Y ServerNet fabrics, provide
redundant, fault-tolerant communications pathways. If a hardware fault occurs on one of the
ServerNet fabrics, communications continues on the other with hardware fault recovery
transparent to all but the lowest level of the OS.
Figure 9-1 is an overview of the modular NSAA and shows one NonStop Blade Complex with
four processors, the I/O hardware and the ServerNet fabrics.
104 Processors and Components: Monitoring and Recovery