Intel S2600KPFR Product Specifications page 131

Technical Product Specification
Most fan implementations provide for a variable speed fan, so the variations in fan speed can
be large. Therefore the threshold values must be set sufficiently low as not to result in
inappropriate threshold crossings.
Fan tach sensors are implemented as manual re-arm sensors because a lower-critical
threshold crossing can result in full boosting of the fans. This in turn may cause a failing fan's
speed to rise above the threshold and can result in fan oscillations.
As a result, fan tach sensors do not auto-rearm when the fault condition goes away but rather
are rearmed for either of the following occurrences:
1. The system is reset or power-cycled.
2. The fan is removed and either replaced with another fan or re-inserted. This applies to
hot-swappable fans only. This re-arm is triggered by change in the state of the
associated fan presence sensor.
After the sensor is rearmed, if the fan speed is detected to be in a normal range, the failure
conditions shall be cleared and a de-assertion event shall be logged.
9.3.13.2 Fan Presence Sensors
Some chassis and server boards provide support for hot-swap fans. These fans can be
removed and replaced while the system is powered on and operating normally. The BMC
implements fan presence sensors for each hot swappable fan. These are instantiated as IPMI
discrete sensors.
Events are only logged for fan presence upon changes in the presence state after AC power is
applied (no events logged for initial state).
9.3.13.3 Fan Redundancy Sensor
The BMC supports redundant fan monitoring and implements fan redundancy sensors for
products that have redundant fans. Support for redundant fans is chassis-specific.
A fan redundancy sensor generates events when its associated set of fans transits between
redundant and non-redundant states, as determined by the number and health of the
component fans. The definition of fan redundancy is configuration dependent. The BMC
allows redundancy to be configured on a per fan-redundancy sensor basis through OEM SDR
records.
There is a fan redundancy sensor implemented for each redundant group of fans in the
system.
Assertion and de-assertion event generation is enabled for each redundancy state.
9.3.13.4 Power Supply Fan Sensors
Monitoring is implemented through IPMI discrete sensors, one for each power supply fan. The
BMC polls each installed power supply using the PMBus* fan status commands to check for
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