Compaq StorageWorks 2100 User Manual page 48

7–2 Model 2100 and 2200 Ultra SCSI Controller Enclosures User Guide
Temperature is monitored by the EMU (see Chapter 3) using an intake air temperature
sensor and stored high-limit temperature settings. If an overtemperature condition is
detected by the EMU, the EMU directs all operational fans to function at high speed,
increasing air flow and cooling throughout the enclosure. When the overtemperature
condition no longer exists, the EMU directs the fans to operate at normal speed.
NOTE: The enclosure cools properly with only two operational fans, provided the third fan or a
blank bezel is installed. However, two defective fans creates an error condition that will develop
an overtemperature condition if not resolved.
Configuration
The enclosure accommodates three fans. A minimum of two operational fans are required.
If the enclosure does not contain an EMU, all fans automatically operate at high-speed by
default. Otherwise, the EMU directs the operating speed of the fans.
Fans are numbered from left to right (Fan 1, Fan 2, and Fan 3 respectively), as viewed
from the front of the enclosure, for error code purposes.
Functionality
Cool air is drawn into the fan module through the bezel and directed into a plenum
(composed of the backplane). The plenum distributes this cooling air to each element.
Each fan operates on +12 VDC supplied from a backplane connector. Fan status and speed
control signals are routed through the backplane to the EMU.
When an error condition exists that involves either the fans, intake air temperature, or
exhaust air temperature, the EMU switches all operational fans into high speed, increasing
air flow throughout the enclosure. This air flow increase permits continued enclosure
operations without data loss or corruption. However, if a second fan malfunctions, air flow
from the remaining fan is insufficient for normal enclosure operations. Unless at least one
of the two defective fans is replaced within 10 minutes, the EMU initiates an enclosure
shutdown.