HP D7171A - NetServer - LPr Manual page 3

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Connectivity
A SCSI interface is an independent and intelligent local I/O bus. Through this bus a variety
of different devices and one or more controllers can communicate and exchange
information. The SCSI interface operates independently of the actions of the rest of the
MBytes/Sec
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40
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0
Figure 2. Storage Controller Maximum
Transfer Rate
technology to extend the current SCSI specifications for cable length, transfer speed and
maximum number of devices per bus. The continued evolution of the SCSI standard and its
on-going implementation in products, make it a cost-effective storage solution, especially
for the entry and mid-range level servers.
Fibre Channel (FC), another connectivity standard, is making inroads into the high-end
Intel-based server market as an alternative to SCSI in configurations in which high
availability, storage scalability and configuration flexibility are demanded. Fibre Channel
provides the user with several improvements over the current connectivity technologies.
The server systems can be cabled over much larger distances, eventually up to
10 kilometers, allowing for mirrored configurations that enhance disaster tolerant scenarios.
The server systems will be more scaleable. SCSI supports a maximum of 15 disks per
channel while up to 126 disks can be attached to a single Fibre Channel arbitrated loop.
Fibre Channel cabling is much easier to use than SCSI cabling since terminators are not
required and thin cables with simple connectors replace thick cables with multi-pin
connectors. Another characteristic that distinguishes Fibre Channel from SCSI is that it is
designed to support a network infrastructure, including hubs and switches. Added to
cabling distance, the networking characteristic gives Fibre Channel tremendous flexibility to
support not only high availability system configurations but also storage networking
applications.
Ultra SCSI Wide Ultra SCSI Wide Ultra2 SCSI (LVD)
system. Many types of peripherals can be
connected along the bus including tape
drives, hard disk drives, scanners,
printers, disk array subsystems, and
CD-ROM drives. Device performance is a
function of the interface data transfer
rates and the saturation of the I/O bus.
Various levels of performance using a
SCSI controller and I/O bus are available
(see Figure 2).
As SCSI technology has evolved, the
server systems benefit by the increased
performance and capability that the most
recent designs provide. The latest step in
the evolution of SCSI is Wide Ultra2 SCSI
which uses low-voltage differential
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