Configuring Your System
AlphaServer 1000A Rackmount Owner’s Guide 6-25
On-Board SCSI Bus Configuration
A fast-wide SCSI-2 controller chip connects directly to the PCI bus to support 16-bit SCSI
devices. The connector is a 68-pin wide connector to the internal fixed drives and to the
5 1/
4
-inch removable-media devices.
Rules for Configuring SCSI Controller Option Cards
All SCSI-2 devices are supported via EISA- or PCI-based SCSI controller cards. Use the
following rules to determine if a SCSI controller or SCSI device can be used on your
system.
•
The controller/device must be supported by the operating system. Consult the software
product description or hardware vendor.
•
In general, when configuring an 8-bit SCSI bus (narrow), up to 7 devices total are
allowed. The entire SCSI bus length, from terminator to terminator, must not exceed
6 meters for single-ended SCSI-2 at 5 MB per second, or 3 meters for single-ended
SCSI-2 at 10 MB per second.
•
When configuring a 16-bit SCSI bus (wide), up to 15 devices are allowed on Windows
NT systems and 7 devices on Digital UNIX or OpenVMS Alpha systems. Bus length
must not exceed 3 meters.
•
For systems running Windows NT, no more than 15 devices can be on any one wide
SCSI-2 controller, for systems running Digital UNIX or OpenVMS Alpha, no more
than 7devices are allowed. Each device must have a unique SCSI ID.
•
If you have two or more controllers on the same bus, you need to change the bus node
ID of the second controller by setting the
pk*0_host_id
environment variable to a
value different from that of the first. Whenever you change the value of this
environment variable, you must initialize the firmware with the
init
command.
SCSI Bus Backplane Configurations
Storage devices are configured in a single-bus configuration. There can be up to four
devices on the same bus as the 5 1/4-inch removable-media device. The bus is driven by a
native Wide SCSI-2 controller on the system board.
Configuring the Backplane with One Controller
The following procedure describes how to connect the three fixed drives to the on-board
controller, which is the same controller that runs the CD-ROM drive and the tape drive, if
one is installed.
