Compaq StorageWorks UltraSCSI RAID Enclosure (DS-BA370 Series) User's Guide (EK-BA370-UG. C02, September 1998)

Introducing the UltraSCSI RAID Enclosure
1–4 UltraSCSI RAID Enclosure
An UltraSCSI Bus Overview
UltraSCSI was developed by Digital Equipment Corporation (now
Compaq Computer Corporation) and subsequently standardized by
the ANSI (American National Standards Institute)
SCSI (small
computer system interface)
committee as standard X3T10.
UltraSCSI is a technology that incorporates several improvements
over a
Fast 10
SCSI bus.
UltraSCSI increases the maximum transfer rate on a wide (16-bit)
SCSI bus from 10
megabits per second (Mb/s)
to 20 Mb/s. This
change increases the maximum bus bandwidth from 20
megabytes
per second
(
MB/s
) to 40 MB/s for a wide (16-bit) SCSI bus.
UltraSCSI incorporates smaller
very high density cable
interconnect
(
VHDCI
) cables and
connectors
. The connector is up
to half the size of the Fast SCSI HD68 (high-density 68-pin)
connector and the cables are thinner.
The higher speed of the single-ended UltraSCSI signals can cause
degradation of signal integrity over the same distances as
single-ended Fast SCSI signals. However, the UltraSCSI bus can run
over much greater distances than Fast SCSI in either single-ended or
differential mode. To attain these greater distances, UltraSCSI defines
and StorageWorks UltraSCSI implements the
bus segment
concept.
An UltraSCSI bus segment is an unbroken electrical path consisting
of conductors (in cables or on
backplanes
) and connectors. Every
UltraSCSI bus segment must have two
terminators
, one at each end
of the bus segment. Bus segments are either single-ended or
differential, depending on the type of terminators used in that
segment. In other words, an UltraSCSI bus segment corresponds to
what Fast SCSI referred to as an entire SCSI bus. As in Fast SCSI, a
bus segment only supports
devices
of the same type as its terminators.
Do not, for example, attempt to use a
differential SCSI bus
device on
a
single-ended SCSI bus
segment.
Note
The Compaq
UltraSCSI RAID enclosure
only supports
single-ended UltraSCSI buses.