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[ The PC Guide | Systems and Components Reference Guide | Hard Disk Drives | Hard Disk Interfaces and Configuration | Small Computer Systems Interface (SCSI) | SCSI Standards | SCSI-3 ]

Overview of SCSI-3 Standards

The SCSI-3 standard is a family of other standards, as I have mentioned. These standards are organized into a structure as defined by the SCSI-3 architecture documents, which categorize the other documents into several groups. On this page I will list, and briefly describe, the documents that make up the SCSI-3 standard family. I am not going to get into too much detail here, as most of these standards will be of only passing interest to the PC user--even one who uses SCSI hardware. :^)

Note: These documents are constantly being updated as a result of ongoing work. While current as of this writing in late 2000, every month documents are revised and change status. For the latest status, or to download drafts of any documents under development, see the T10 technical committee web site or the other web sites referenced below.

The first group are the command sets, which define commands used for various SCSI commands. These include the following:

Command Set

Description

Document

Abbreviation and Generation

Status

Standard or Project

Shared

Commands defined for all SCSI devices

SCSI-3 Primary Commands

SPC

Published

X3.301-1997

SPC-2

Pending Publication

T10 1236-D

SPC-3

Development

T10 1416-D

Block

Commands defined for random-access devices that transfer data in blocks, such as hard disks

SCSI-3 Block Commands

SBC

Published

NCITS.306-1998

SBC-2

Development

T10 1417-D

Block
(Reduced)

A "simplified" version of the block command set

SCSI-3 Reduced Block Commands

RBC

Published

NCITS.330-2000

Stream

Commands for streaming, sequential-access devices such as tape drives

SCSI-3 Stream Commands

SSC

Published

NCITS.335-2000

SSC-2

Development

T10 1434-D

Medium Changer

Commands for medium-changing devices such as tape or disk "jukeboxes"

SCSI-3 Medium Changer Commands

SMC

Published

NCITS.314-1998

SMC-2

Development

T10 1383-D

Multimedia

Commands for "multimedia devices" (typically, optical drives)

SCSI-3 Multimedia Commands

MMC

Published

X3.304-1997

MMC-2

Published

NCITS.333-2000

MMC-3

Development

T10 1363-D

Multimedia
(Reduced)

A "simplified" version of the multimedia command set

SCSI-3 Reduced Multimedia Commands

RMC

Development

T10 1364-D

Controller

Commands for RAID controllers

SCSI-3 Controller Commands

SCC

Published

X3.276-1997

SCC-2

Published

NCITS.318-1998

Enclosure Services

Commands for SCSI device enclosures

SCSI-3 Enclosure Services

SES

Published

NCITS.305-1998

Object Based Storage Devices

Defines an object-oriented command set for accessing data

Object Based Storage Device Commands

OSD

Development

T10 1355-D

The other two groups of standards are protocols and interconnects. Protocols define how data is interchanged, and transports describe the physical ways that protocols are implemented. They are closely related and in some cases now are defined by a single document, which makes them a bit difficult to present in an organized way. I will start by discussing the various protocols (also called transports by some):

Protocol

Description

Document

Abbreviation and Generation

Status

Standard or Project

Interlocked (Parallel Bus)

Defines the protocol for "regular" parallel SCSI

SCSI-3 Interlocked Protocol

SIP

Withdrawn; now incorporated into later versions of the SCSI-3 Parallel Interface

--

Fibre Channel

Defines the protocol for running SCSI on the Fibre Channel interface

SCSI-3 Fibre Channel Protocol

FCP

Published

X3.269-1996

FCP-2

Pending Publication

T10 1144-D

Serial Bus

Defines the protocol for transporting commands over the IEEE-1394 (serial) interface

Serial Bus Protocol

SBP

Withdrawn

--

SBP-2

Published

NCITS.325-1998

Serial Storage Architecture

Defines the transport layer for Serial Storage Architecture, an advanced interface used in servers and enterprise hardware; there are two documents that specify the protocol

Serial Storage Architecture SCSI-3 Protocol

SSA-S3P

Published

NCITS.309-1998

Serial Storage Architecture Transport Layer

SSA-TL2

Published (replaced SSA-TL1)

NCITS.308-1998

Finally, this table shows the interconnect standards, also sometimes called physical layer documents (since they describe how devices are physically connected):

Interconnect

Description

Document

Abbreviation and Generation

Status

Standard or Project

Parallel Bus

Describes the electrical signaling, connectors and related issues associated with "regular" parallel SCSI; starting with SPI-2 these include the formerly separate SIP protocol document

SCSI-3 Parallel Interface

SPI

Published

X3.253-1995

Fast-20 (addendum to SPI)

Published

X3.277-1996

SPI-2

Published

X3.302-1999

SPI-3

Pending Publication

T10 1302-D

SPI-4

Development

T10 1365-D

Fibre Channel

Several documents define alternative physical layer standards for Fibre Channel; these are maintained by the T11 technical committee and include Fibre Channel Arbitrated Loop (FC-AL) and several revisions of the Fibre Channel Physical Interface (FC-PHx)

Serial Bus

The physical layer standards for the serial bus (IEEE-1394) are developed by the IEEE High Performance Serial Bus Bridges Working Group (P1394)

Serial Storage Architecture

Defines the physical connections for the Serial Storage Architecture interface

Serial Storage Architecture Physical Layer

SSA-PH

Published

X3.293-1996

SSA-PH2

Published

NCITS.307-1998

Whew. Well, you can certainly understand now why some people find SCSI-3 "a bit confusing". :^) I hope that this "road map" helps to make things a bit more clear for my readers though!

Next: SCSI(-3) Parallel Interface (SPI)


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