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Chapter 2 System Overview 23
Hardware Watchdog Mechanism and XIR
To detect and respond to system hang conditions, the Sun Fire V490 system features
a hardware watchdog mechanism—a hardware timer that is continually reset as long
as the operating system is running. In the event of a system hang, the operating
system is no longer able to reset the timer. The timer will then expire and cause an
automatic externally initiated reset (XIR), eliminating the need for operator
intervention. When the watchdog mechanism resets the system after sending
information to the screen and depending upon the OBP variable, a core file might be
created to give additional information.
Note – The hardware watchdog mechanism is not activated until you enable it. See
“How to Enable the Watchdog Mechanism and Its Options” on page 156 for
instructions.
The XIR feature is also available for you to invoke manually, by way of your RSC
console. You use the xir command manually when the system is absolutely hung
and an L1-A (Stop-A) keyboard command does not work. When you issue the xir
command manually by way of RSC, the system is immediately returned to the
OpenBoot PROM ok prompt. From there, you can use OpenBoot commands to
debug the system.
Dual-Loop Enabled FC-AL Subsystem
The system’s dual-ported Fibre Channel-Arbitrated Loop (FC-AL) disk drives and
dual-loop enabled FC-AL backplane may be combined with an optional PCI FC-AL
host adapter card to provide for fault tolerance and high availability of data. This
dual-loop configuration allows each disk drive to be accessed through two separate
and distinct data paths, providing both increased bandwidth and hardware
redundancy; that is, dual-loop configuration provides the ability to sustain
component failures in one path by switching all data transfers to an alternate path.
The FC-AL subsystem is described in greater detail in:
■ “About FC-AL Technology” on page 41
■ “About the FC-AL Backplane” on page 43
■ “About the FC-AL Host Adapters” on page 44