Acer SmartRAID V Bedienungsanleitung Seite 194

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Theory of Operation
On-Board Microprocessor
SmartRAID V controllers use embedded processors to maximize their
performance when installed in fully loaded servers. The onboard
microprocessor performs high-level processing of commands from the
host and controls the sequencing of command execution on the controller.
A fast microprocessor enables the controller to process more I/O
commands per second which is especially important when caching and
RAID are used.
SmartRAID V Millennium controllers use a high-performance RISC
processor. SmartRAID V Decade and Century controllers use an Intel
i960
®
embedded I/O processor.
SCSI Interface
The Small Computer Systems Interface (SCSI) is a standard parallel
interface designed to communicate with intelligent peripheral devices.
SmartRAID V controllers conform to the ANSI SCSI specification defined
in ANSI document number X3.131-1986 and subsequent standards defined
in ANSI X3.131-1994 (SCSI-2) and various SCSI-3 specification documents.
SCSI Device IDs
The original SCSI specification allowed up to eight SCSI devices, including
the controller, to be connected to a single 8-bit SCSI bus. Wide (16-bit)
SCSI busses support up to fifteen devices and one controller per bus. All
SCSI devices, including the controller, must be assigned a unique numeric
identifier. These SCSI IDs can be any number from 0 7 or, for Wide SCSI
devices, 0 15. The SmartRAID V controller ID is set by default to ID 7.
In 8-bit SCSI systems, the device with ID 7 has the highest priority and ID
0 has the lowest priority when arbitrating for use of the SCSI bus. In a
Wide SCSI system, IDs have the following priority (highest to lowest):
7, 6, 5, 4, 3, 2, 1, 0, 15, 14, 13, 12, 11, 10, 9, 8
The IDs 8 15 always have a lower priority during arbitration than 8-bit
devices, this allows 8-bit devices which do not recognize IDs 8 15 to
coexist on a SCSI bus with Wide SCSI devices which may be assigned
those IDs. However, when controlling 8-bit devices, a Wide SCSI controller
cannot be assigned an ID greater than 7 because 8-bit devices would not
be able to recognize the controller.
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