Data General AViiON 4600 Series, Customer Documentation

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Setting Up and Installing a SCSI Bus
014–002091
4-3
Identifying SCSI Drives
Each SCSI controller in your computer unit can support a total of seven SCSI devices,
including internal devices such as tape and disk drives. For example, if your computer
includes one tape drive and one SCSI disk on the first bus, you can connect five
additional devices to that (Controller 0, SCSI A) bus. If your computer unit includes
three internal devices, you can connect only four external devices to the SCSI A bus;
the maximum of four internal drives reduces the maximum number of external drives
the bus could support to three. Since it does not support internal drives, the second
(Controller 1, SCSI B) bus can support seven external SCSI devices. When a single
mass-storage subsystem contains multiple drives, each individual drive applies to the
seven-device maximum.
Each individual drive on a SCSI bus must have a unique SCSI identification number
(also referred to as a
SCSI ID, device ID , or DID ) with a value from 0 through 6.
When you receive preinstalled devices mounted either inside the computer unit or
mounted inside a mass-storage housing unit, the SCSI ID numbers are already set. If
you add or replace devices anywhere on the SCSI bus, you must set the IDs by
positioning drive-select jumpers on the individual device(s).
Table 4-1 lists the default (factory-installed) SCSI device ID numbers for hard disk,
diskette, and tape drives. The DG/UX Device Name" column lists the mnemonic
name that the DG/UX operating system and the computer system firmware use to
identify a device on the first (controller 0) bus in your system; the mnemonic name
includes the SCSI ID of the device.
Table 4–1 Default SCSI Device ID Numbers
1
Includes diskette, optical disk, and CD-ROM drives.
2
The SCSI ID of a diskette drive is set on a SCSI adapter board, not on the drive. If you have more
than one diskette drive managed by the same SCSI adapter board, the drives have the same SCSI ID
number. The LUN (Logical Unit Number) differentiates drives managed by the same SCSI adapter.
Drives ID Number DG/UX Device Name
Disk
1
First 0
Second 1
Third 2
Fourth 3
Diskette
First (Diskette LUN 0) 1, 2, or 3;
determined
x
Second (Diskette LUN 1)
as next sequential disk (x)
x
Cartridge Tape
First 4
Second 5
Third 6