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14 High Availability Software for the Intel
®
NetStructure
TM
ZT 4901 Technical Product Specification
Introduction
Split Mode—Split Mode is a term that refers to a system operating with multiple system master
Host boards that each own a single bus segment. Split Mode may refer to either Active/Active or
cluster modes. In an Active/Active either of two Hosts can inherit the other Host’s bus segment. In
cluster mode each Host’s bus segment is locked to that Host and ownership cannot be transferred to
the other Host.
Standby Host (also known as the standby system master)—System board in a High Availability
system that is currently operating in Drone Mode and therefore not the Active Host. The Standby
Host has no visibility of the devices on the other side of the PCI-to-PCI bridge.
Switchover—Changing ownership of a domain from one Host to another.
System Host functions—Central functions provided to a CompactPCI bus segment including hot
swap event response, bus enumeration, and interrupt service. The system slot board provides these
functions.
System slot—Slot occupied by a System Master that performs arbitration for secondary bus
masters, responds to interrupts from peripheral boards, and drives a clock signal to each backplane
slot.
Takeover—A type of switchover that is initiated by the Standby Host in a High Availability
system. A takeover may be hostile or friendly.
Warm Switchover—A warm switchover refers to the state of the domain that is being inherited by
the Host taking ownership. On a warm switchover domain ownership is transitioned and, before
any bus actions or operations are allowed to occur, the bus segment is toggled through reset. This in
effect resets all the devices that reside in the reset domain.
2.2 High Availability Hardware Approach
In an RH system the Redundant System Slot (RSS) subsystem is spread across several building
blocks. These include:
• Processor boards (such as the Intel
®
NetStructure™ ZT 5524 System Master Processor Board)
• Bridge mezzanine (such as the Intel
®
NetStructure™ ZT 4901 Mezzanine Expansion Card)
• Backplane (such as the Intel
®
NetStructure™ ZT 4103 Redundant Host Backplane)
Other building blocks and subsystems may be required to support the RSS subsystem. These
include:
• System management
• Storage
• Power distribution
• Cooling
• Media
• Packet switching