scsi technology

SCSI Technology

Black Box Corp.Dave Mueller

International Tech SupportDecember 2000

http://www.blackbox.com/techsupport/tchsupportindex.htm

BB Brasil Training December 2000 2

History of SCSI

• IBM-360 Selector Channel• SASI

– 1979 Shugart Assoc. Systems Interface• Scaled down version of the IBM Interface

– 1981Submitted to ANSI X3T9.2 committee

• SCSI– X3.131-1986– Approved in 1986


SCSI Generations• SCSI 1 and SCSI 2

– Each version was a complete specification

– Narrow bus, slow speeds

• SCSI (formerly SCSI 3)– SPI SCSI Parallel Interface

• A collection of standards

• Wide bus on single connector, higher speeds

• Makes older standards (SCSI 1, 2) and features (HVD) obsolete

– SBP Serial Bus Protocol (IEEE1394)

– FCP Fibre Channel Protocol (Fibre Channel)

– SSA Serial Storage Architecture (IBM)


SPI• SPI (SCSI-3)

– 10MBps (narrow) or 20MBps (wide)

– Ultra (Fast-20) is a half standard• Includes SPI but up to 20/40MBps (narrow/wide)

• SPI-2 (Ultra2)– LVD, SCA-80, VHDCI

– 20/40MBps

• SPI-3 (Ultra3)– Makes HVD and dual-cable wide bus (SCSI2) obsolete

– WIDE only

– 160MBytes/sec

– Many technical refinements (timing, command structure)


Single Ended vs. Differential• Single Ended

– Low cost– Short cable length

• 1.5m @ 20 MBps, 3m @ 10 MBps, 6m @ 5 MBps

– Most Common– Internal cables are flat ribbon

• Differential– Expensive– Long cable lengths

• HVD 25m at all speeds, LVD 12m at all speeds

– Usually only on high end products (RAID array)– Internal cables must be flat twisted pair ribbon


LVD vs. HVD• HVD

– Originally in SCSI 1 (“differential”)

– Defined in SCSI 2 as HVD

– Made obsolete in SPI-3

– 25 Meters

• LVD– Defined in SPI-2

– 12 meters

– Backwards compatible with old SINGLE ENDED devices• Bus can only function in one mode, LVD (12m) or Single Ended (1.5/3/6m)

• LVD Host adapter to legacy SCSI devices

• If any device is legacy SCSI SE, then all LVD devices function as SE only


Ultra3 SCSI

Wide Ultra2 SCSI

Ultra2 SCSI

Wide Ultra SCSI

Wide Ultra SCSI

Wide Ultra SCSI

Ultra SCSI

Ultra SCSI

Fast Wide SCSI

Fast SCSI

SCSI-1

STA Terms

6

2

2

2

2

2

N

O

T

E

16(5)12(4)16160

162512(4)1680

82512(4)840

4--31640

8--1.51640

1625(3)-1640

8--3820

825(3)1.5820

1625(3)31620

825(3)3810

825(3)685

HVDLVDSingle Ended

Maximum Devices

Max Bus Length

Meters (1)Bus Width

Bits

Bus Speed

Mbytes/Sec

STA Terms


Notes(1) The listed maximum bus lengths may be exceeded in Point-to-Point and engineered

applications.

(2) Use of the word "Narrow", preceding SCSI, Ultra SCSI, or Ultra2 SCSI is optional.

(3) LVD was not defined in the original SCSI standards for this speed. If all devices on the bus support LVD, then 12-meters operation is possible at this speed. However, if any device on the bus is singled-ended only, then the entire bus switches to single-ended mode and the distances in the single-ended column apply.

(4) Single-ended is not defined for speeds beyond Ultra.

(5) HVD (Differential) is not defined for speeds beyond Ultra2.

(6) After Ultra2 all new speeds are wide only.

Chart and notes copied from SCSI Trade Association


SCSI 1

• 5 MBytes/Second, 8 Bits wide

• Electrical– Single Ended

• Logic 1 = 0.0 to 0.5 VDC

• Logic 0 = 2.5 to 5.25 VDC

– Differential (HVD - High Voltage Differential)• Logic 1 = +Signal > -Signal

• Logic 0 = -Signal < +Signal


SCSI 1 Connectors

• ‘A’ Cable– Alternative 1

• Unshielded 50 Pin, latches optional– Internal Ribbon, AMP-LATCH

• Shielded 50 Pin (AMPMODU)

– Alternative 2• Shielded 50 Pin (External Telco, 50 pin Centronics,

CHAMP)


SCSI 2

• X3.131-1994

• Defines 8, 16 and 32 bit bus

• Defines “Fast” SCSI for 10, 20 and 40 Mbytes/second

• Adds the high density (.050 inch) 50 and 68 pin connectors


SCSI 2 Connectors

• ‘A’ Cable– Alternate 1

• Unshielded HD 50 pin, no hardware

• Shielded HD 50 pin with latches

– Alternate 2• Unshielded LD, no hardware (50 pin ribbon)

• Shielded LD with latches (50 Pin Centronics)


SCSI 2 Connectors

• ‘B’ Cable– Carries only high bytes

• ‘A’ cable required for low bytes & termpwr

– Unshielded HD 68 pin, no hardware– Shielded HD 68 pin, latches


SCSI 3

• X3T10 Committee• A collection of substandards• SCSI Parallel Interface (SPI)

– Extension of SCSI 2

• Serial– Fibre Channel– Serial Bus Protocol 2 (IEEE1394-1995)– IBM SSA (Serial Storage Architecture)


SCSI 3

• Ultra2 and Wide Ultra2– 40M and 80MByte/sec

• Ultra3– 160MByte/sec


SCSI 3 Connectors

• ‘P’ Cable– Unshielded HD 68 pin, no hardware– Shielded HD 68 pin, 2-56 screws– Carries control and 16 bits of data

• ‘Q’ Cable– Same connectors as the ‘P’ Cable– Used for high bytes in 32 bit systems

• ‘P’ cable required for low bytes & termpwr


Interconnections

• Narrow to Wide– Terminate high bytes

• Do NOT mix single ended and differential

• Do NOT mix HVD and LVD

• Customer must know their application

• See warning in AMP SCSI Guide


SCSI Connectors• SCSI 1

– Internal: 50 Pin IDC Ribbon– External: Centronics

• SCSI 2– Includes SCSI 1– Adds MD50 for external (MD for Micro D)

• SCSI 3– Includes SCSI 1 and 2– Adds MD68 for external (screw locks) and internal (no

locks)• SPI-2

– Adds VHDCI (Very High Density 68 pin) for external


Black Box Products• Cables and Terminators

– Dead-end and pass through– High Line– Active, passive, forced perfect

• Differential ALWAYS passive, LVD is intelligent terminator

• Adapters– Does customer need adapter or High Line Terminator?

• Converters– SE to HVD, SE or HVD to Fiber Optic

• Repeaters• Switches• Host Adapters

– IC510C is ISA, all others are PCI


Host Adapters

MD68MD6816LVDUltra280IC515C

IDC50

MD68MD6816SE

Wide Ultra

40IC514C

2xIDC50

2xMD681xMD6816SE

Wide Ultra

40IC513C

IDC50MD508SEUltra20IC512C

IDC50MD508SEFast10IC511C

IDC50DB25 (Mac)

8SEFast10IC510C

Int ConnExt ConnBus WidthSE/DiffSCSIMax Speed

Mbytes/S


Web Sites• T10 Committee Website www.t10.org• SCSI Trade Association www.scsita.org• www.adaptec.com• www.amp.com• www.ancot.com• www.apcon.com• www.fibrechannel.com• www.paralan.com• www.timberconn.com• www.scsimasters.com

http://www.scsimasters.com/

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