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Oracle Tips by Burleson |
Disk I/O Tuning
Chapter 2:
SCSI
Interfaces
Depending on implementation, the command groups may vary in
definition and grouping, but the essentials remain the same. SCSI-3,
now more commonly called ANSI SCSI, is what now constitutes the
"SCSI" definition (and the command set listed above). Note that for
a number of commands sets listed above, second generation proposals
are now in the works. Such proposals, such as SBC-2, will be
backwards compatible.
The
commands (above) all fall under the mantle of "SCSI Block Commands"
(SBC). The SCSI Primary Commands (SPC) set sits over these more base
commands, providing the basis for SCSI interoperability--therefore,
per the SCSI-3 specification, all SCSI devices must support SPC,
otherwise the dream of true interoperability is not possible.
Together, these two "units" serve as the command base for all SCSI
controller hardware. With the introduction of Fibre Channel and
SCSI-3, the protocol layer has been forced to branch into several
directions. It is the job of the SCSI controller to handle the
appropriate protocol path -- SCSI Interlocked Protocol serving the
more common, SCSI Parallel interface, and SCSI Fibre Channel
Protocol handling Fibre Channel requests. Prior to SCSI-3, the
protocol would have tied directly to the SCSI Parallel Interface.
This is illustrated in Figure 2-2.
Figure 2-2: SCSI Architecture
SCSI
3 is the latest commonly available implementation of SCSI, let's
examine it in more detail.
The above text is
an excerpt from:
Oracle Disk I/O Tuning
Disk IO Performance & Optimization for Oracle
Databases
ISBN
0-9745993-4-4
by Mike Ault
Oracle Consulting
Services
Burleson
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