Intel SPSH4 - Server Platform - 0 MB RAM, Технические характеристики продукции

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SCSI Bay Boardset SPSH4 Server System External Product Specification
Revision 1.11 52
6.1.1 Architectural Overview
The drive backplane is an integral part of the system chassis. It is designed to provide a cost
effective ease of power-on (Hot Swap) drive replacement. It also provides easy RAID integration
over a wide range of RAID controller products. It is designed to be vendor independent.
The feature that simplifies RAID integration is the addition of an on-board SCSI target whose
command set allows vendor independent controller management and monitoring for associated
drive functions such as: Drive insertion and removal, light indicators, and drive power control. Its
use simplifies cable management and eliminates errors caused by the possibility of incorrect
correlation of several cables.
The LVD/SE SCSI Backplane performs the tasks associated with hot-swappable SCSI drives,
and enclosure (chassis) monitoring and management supported by the LVD/SE SCSI
Backplane. They include, but are not limited to, the following:
•
Monitoring the SCSI bus for enclosure services messages, and acting on them
appropriately. Examples of such messages include:
- Activate a drive fault indicator
-
Power down a drive, which has failed
-
Report fan tachometer status
•
SAF-TE intelligent agent, which acts as proxy for “dumb” I
2
C devices (that have no bus
mastering capability) during intra-chassis communications.
6.2 Design Constraints and Assumptions
This section specifies certain assumptions and limitations taken into consideration during the
design of the LVD/SE SCSI backplane.
6.2.1 SCSI Bus Considerations
The SCSI bus is based on the SPI-4 specification. It is designed to allow any SCSI device to
communicate with any other SCSI device. To that end, SPI-4 requires that all SCSI devices be
at certain distances apart, depending on the media capacitance measured in pF/m. The lower
the media capacitance the greater the spacing needs to be because the loading from the device
becomes more significant.
Historically, backplane designs have successfully violated this guideline because of careful
simulation backed up with signal integrity validation. Those past designs were able to have
straight-to-straight connections between three devices with some meandering between another
three devices. The layout and board stackup was driven from LVD SCSI bus simulation, which
yielded the following:
• SCA-2 to SCA-2 electrical distance of four inches
• Six-layer board with two internal SCSI layers with 90 Ohm impedance targeted
•
Total backplane SCSI length max 30 inches
The electrical spacing of the SCA-2 connectors was a combination of the faster edge rate and
faster transfer speed.
The following are key points to know: