This appendix describes the Small Computer Systems Interface (SCSI). Topics covered in this appendix include:
There are two micro-miniature SCSI ports on the back panel of a DDP. The SCSI connectors have 50 pins divided into two rows. You can connect the DDP your system in two ways - direct connection or daisy-chain.
If fast SCSI devices and old-style connectors must be used in the same system, the old-style connectors should be connected to a separate SCSI port that doesn't contain fast SCSI devices. Do not connect fast SCSI devices and old- style connectors in the same daisy chain. Old-style connectors can be identified by a 3-row 50-pin D connector, a 50-pin ribbon style connector, or a 50-pin "Centronics style" of a connector (1/2-inch FCT).
You can connect the DDP to your system in two ways - direct connection or daisy-chain. Connecting the SCSI cable of the DDP to the SCSI port of your system is a direct connection. Connecting the SCSI cable of the DDP to the SCSI port of another SCSI device is a daisy-chain.
Use direct connection when you are connecting the first SCSI device in the SCSI bus to the desktop computer system by connecting one end of the SCSI cable to one of the SCSI ports of the DDP, and the other end of the SCSI cable to the SCSI port of the desktop system. You must connect a regulated SCSI terminator to the other SCSI port of the DDP, as illustrated in Figure B-1.
Figure B-1 An Example of a Direct Connection
Note - If you install a SBus card with an additional SCSI port in the desktop system, you can connect the DDP to the SCSI port of the SCSI card.
To set up a DDP in a direct connection, perform the following procedure:
Allow at least 3 inches (76mm) between the DDP and the desktop system for ventilation and for access to the diskette drive in your system.
Figure B-2 Placement of Desktop Disk Pack
If you need to disconnect a SCSI cable or terminator, press in on the clips on the sides of the connector and pull the connector out of the SCSI port.
If the DDP is being installed with other SCSI devices, you must replace any of the older, passive terminators with the regulated terminator.
A daisy-chain is a means of connecting a number of SCSI peripherals to a host system. A daisy--chain allows a single port on the desktop system to connect to more than one SCSI peripheral. If you want more than one SCSI peripheral on a bus, you need to daisy-chain.
Note - Devices with the old-style connectors (3-row 50-pin D connectors or 50- pin ribbon connectors) should not be used on the same bus (daisy-chained) with fast SCSI devices.
If you connect SCSI devices to your system in this manner, connect a regulated terminator to the unused SCSI port on the back panel of the last device in the daisy-chain, as shown below:
Figure B-3 An Example of a Daisy-Chain Connection
To set up a DDP in a daisy-chain connection, perform the following procedure:
Make sure the total SCSI cable length does not exceed 6 meters (20 feet).
A bus is a signal route to which several parts of a computer system may be connected so that signals can pass between them. The total length of a SCSI bus includes:
Your desktop system performance is reliable with a maximum SCSI bus length of 20 feet (6 meters), as illustrated below. The internal signal path of your system unit and the external SCSI cables must not exceed this maximum length. If this length is exceeded, the system will not run in a reliable manner.
For example, suppose you wish to connect a DDP and a Desktop Storage Module to a SPARCstation 2 system. This configuration would have a total (internal and external) SCSI bus length of 1.9 meters (as indicated below).
Since the total - added to the length of the external cables - is well below the maximum of 6 meters, this configuration is acceptable.
Table B-1 lists the SCSI cable lengths and the internal SCSI buses for the DDP and your system. When connecting the DDP to your system, find the total SCSI bus length for your configuration. To do this, add the cable and internal bus lengths for the system and each device. This total length must be less than 20 feet (6 meters).
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Devices and Cables SCSI Cable Length Inches Meters ------------------------------------------------------------------------------
Devices, Internal Cables:
Desktop Disk Pack 0.3 13
SPARCstation 2 0.5 20
SPARCstation 10 0.9 35
SSHA, SBE, FSBI 0.1 4
External SCSI Cables:
Desktop Disk Pack Cable
(to connect to a desktop system or to
daisy chain a second DDP to the first
on a 630 or 670)
Desktop Disk Pack Cable
(to connect external devices to
630/670)
0.8 32
2.0 79
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This totals 2.7 meters of cable, less than the 6 meter maximum for each SCSI bus.
This totals 3.1 meters of cable, less than the 6 meter maximum for each SCSI bus.
This totals 2.7 meters of cable, less than the 6 meter maximum for each SCSI bus.
This totals 4.7 meters of cable, less than the 6 meter maximum for each SCSI bus.
If the SCSI bus length exceeds 6 meters, install some of the devices on additional SCSI buses by installing an SBus SCSI Host Adapter card (SSHA) or a FSBE/S with desktop systems or an SBE/S SBus card with deskside systems. The SBus SCSI Host Adapter card provides an additional SCSI port (SCSI bus) for your system. The SBE/S or FSBE/S SBus card provides an additional SCSI port and an Ethernet port.
When you insert an SBus SCSI Host Adapter card into your system, the SCSI bus length total does not include the internal cable length of the system, listed in Table B-2. For example, if you have a SPARCstation IPC and are connecting two Desktop Storage Modules and two DDPs to the SBus SCSI Host Adapter card of the system, you need to add the following cable lengths:
This totals 4.4 meters of cable length, less than the 6 meter maximum for each SCSI bus. Note that you do not include the internal bus length of the SPARCstation IPC (0.5 meters).
Additional SCSI buses, SCSI bus 1, 2, 3, and 4 are named based on the order they are found by the OpenBoot(TM) PROM when probing SBus slots. SBus slots are probed in this order: on-board, slot 0, slot 1, slot 2, slot 3.
For example, if the first FSBE/S SBus card is in slot 2, when the system probes the SBus slots, it begins probing the on-board SCSI bus, then SBus slot 1, then SBus slot 2, and so on. Because slot 2 contains the first FSBE/S SBus card, this is SCSI bus 1. As Table B-2 illustrates, SCSI bus 1 supports disk, tape, and CD-ROM.
Table B-2 Devices Supported With Additional Single-ended SCSI Buses (SunOS 4.1.x)
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SCSI Bus Number Device --------------------------------------------
SCSI bus 1, first FSBE/S SBus card Disk
Tape
CD-ROM
SCSI bus 2, second FSBE/S SBus card Disk
SCSI bus 3, third FSBE/S SBus card Disk
Tape
CD-ROM
SCSI bus 4, fourth FSBE/S SBus card Disk
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Note - For the Solaris 2.x operating system, disk, tape and CD-ROM devices are supported on all SCSI buses
You must attach a regulated SCSI terminator to the SCSI port at the end of the SCSI bus. A terminator holds the bus at a predetermined signal level when the bus is not active and maintains impedance matching.
All SCSI daisy chains must be terminated at the last units attached to the SCSI bus. A terminator is built in to all SBus SCSI cards and to all host systems. The regulated terminators must be used for all 50-pin SCSI busses having fast SCSI drives on a fast SCSI host.
Figure B-4 Regulated and Nonregulated Terminators
Follow these SCSI Termination rules:
Devices with the 3-row 50-pin D connector or the 50-pin ribbon connector (old- style connectors) should not be used on the same bus with fast SCSI devices.
Note - The mixing of fast SCSI devices and old-style connectors in the same daisy chain is not recommended since errors may be created and performance may be degraded.
If fast SCSI devices and old-style connectors must be used in the same system, the old-style connectors should be connected to a separate SCSI port that doesn't contain fast SCSI devices.
If you are running SunOS 4.1.2 or an earlier version and use a fast SCSI bus, system performance is not affected. If you are using SunOS 4.1.3 (Solaris 1.1) or a later version with a fast SCSI bus, you must turn off the fast bus or performance will be degraded.