Technical information

configuration information for the enclosure and to set and sense standard bits for each type of element
that may be installed in the enclosure. Since the SES unit communicates over the SCSI Bus, it consumes
a SCSI ID.
In the event of an SES failure, no data is lost and no disks become unavailabe . What is lost is the
information pertaining to the status of power supplies, fans, and temperature within the enclosure. In
addition, the information about the configuration of the enclosure, (which disk slots are occupied, which
are empty) will be unavailable. Finally, the ability to control the red disk LED will be absent and any
LEDs which were lit will be dark. During the failure or absence of the SES unit, the fans will run at full
speed (100%) regardless of temperature.
Like the SES unit, the SE-SE I/O repeater and terminator module slots are located on the rear of the disk
shelf. There are two slots dedicated for the modules, and either slot can be used for the SE-SE I/O
repeater module or the termination module.
The SCSI bus is single-ended, FAST/WIDE (20MB/sec). Due to physical and cabling restraints, the
SE-SE I/O repeater module is needed to ensure enough margin of the signal integrity. It allows the SCSI
Bus to be extended 3 meters from the connector.
When the SE-SE I/O repeater module is plugged into the disk shelf, the backplane, disks, SES unit, and
terminator module all operate in SE mode. The SE-SE I/O repeater module effectively cuts the SCSI bus
in half, making two physical busses behave as a single logical bus. Since the SE-SE I/O repeater is an
integral component of the SCSI bus, a failure results in a loss of connection to the disks. Connection
from the outside world to the internal backplane SCSI bus is through the repeater module.
The terminator module installs into one of the I/O slots located on the rear of the shelf. For consistency,
it is installed in the slot closest to the input power connector.
The terminator module is a multi-mode terminator. It operates in SE mode and provides automatic
termination of the SCSI Bus on the backplane.. Since the terminator module is an integral component of
the SCSI Bus, a failure results in a loss of connection to the disks. It is not hot-swappable. Pulling the
terminator causes the SCSI Bus to become disabled.
There are two green LEDs located on the terminator module. The one marked SE should be on to
indicate the SCSI Bus is operating in SE mode.
5.3.3 Disk Configurations
The disk drives are controlled by the U501 PCI SCSI controllers configured as dual-initiated Host Bus
Adapters (HBAs).
The following table shows the disk shelf enclosure slot assignments.
Slot #
8 7 6 5 4 3 2 1 0
Component
PS 1 PS 0 Disk 6 Disk 5 Disk 4 Disk 3 Disk 2 Disk 1 Disk 0
The table below shows the SCSI IDs for the disk drives and SES unit.
Slot #
8 7 6 5 4 3 2 1 0
SES Unit
Theory of Operation
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