Technical information

5.3.2 Disk Enclosure Components
The disk shelf backplane is the heart of the enclosure. It distributes the SCSI bus and power to all of the
drives and provides the interconnection between all other modules that are plugged into it. The disk slots
bring the SCSI bus and power connections to each disk drive. Each slot has two LED’s associated with it.
The first is a green LED that is driven by the LED_OUT signal directly from the drive, and the second is
a red LED driven by the SES unit. There is also a Drive_Present signal that is monitored by the SES
Unit. This signal is used to detect the presence or absence of individual disk drives within the enclosure.
The power supplies are installed from the front of the shelf. They are 2N supplies providing fault
tolerant power and are rated for a high output of 260 watts max./300 watts peak. The power supplies are
located at the two left-most slots of the disk enclosure. These slots are dedicated as power supply slots
only; a disk drive cannot be inserted into these slots. The input power for these slots is individually
connected to the mains input connector. The green LEDs for these slots are driven by the power supply
present signal from each of the respective power supplies. The green LED will not light if the input
power to the power supply is not present. These LEDs indicate that the power supplies are receiving
good input power. The red LEDs for these slots are driven individually by the SES unit. These LEDs
indicate that the power supply is broken, and is not supplying its share of power to the load.
The disk drives are 16-bit wide single-ended SCA-2 drives manufactured by Seagate. They have the
following features:
Rotational speed of 10,000 RPM
●
Operate at 20 MB/sec (Fast/Wide) SCSI●
Direct connect to backplane via SCA-2 connector (no internal flex cables)●
Fault and status indicators●
Single button release●
One piece aluminum canister ●
Disk firmware is downloadable●
(PRML) read channel electronics●
Embedded servo technology●
Wide Ultra2 SCSI interface●
Dual Stripe Magneto-Resistive (DSMR) Head Technology, which provides a differential signal, to
reduce noise.
●
Higher density media for increased BPI (bits per inch)●
MTBF (Mean Time Between Failures) of the disk drives is 300K hours.
The SES unit is located on the rear of the disk enclosure. The SES unit provides continuous monitoring
and control of the disk shelf. It is responsible for monitoring the disks, power supplies, fans, and
temperature of the shelf. It also controls various LEDs and the fan speed.
The SES unit reports status to the host and receives control information via the SCSI bus (per the SCSI-3
Enclosure Services Specification) as opposed to a separate cable. It accomplishes this task by using the
SCSI SEND DIAGNOSTIC and RECEIVE DIAGNOSTIC RESULTS commands to obtain
Theory of Operation
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