DEC AlphaServer 2100, Owner'S Manual

Page: 124 / 192

SCSI Buses
The system supports up to two internal StorageWorks shelves
that can each support up to eight SCSI disk drives in a dual-bus
configuration.
Configuring
the Removable
Media Bus
Removable-media storage devices should only be installed by a
qualified service person.
Warning
Before connecting removable-media SCSI devices to your
system, turn off all power to the system (both AC and
DC). Refer to ‘‘Powering Down the System’’ in Chapter 1
for information about turning off AC and DC power.
The removable-media bus can be configured to extend into an
internal StorageWorks shelf or to allow expansion from the
connector on the bulkhead at the rear of the enclosure:
• When the bus is configured to extend into an internal
StorageWorks shelf (Figure 3–6), the bus must be terminated
at the bulkhead connector using the external SCSI
terminator (12-37004-04).
External expansion from the back of the enclosure is not
allowed in this configuration, as it would violate SCSI bus
length rules.
• When the bus is not extended into an internal StorageWorks
shelf, the internal SCSI terminator (12-41296-01) is required,
as shown in Figure 3–6.
External expansion from the back of the enclosure is
available in this configuration; however, the connecting
cable cannot exceed 1.5 meters in length. If the bus
is not expanded, be sure the external SCSI terminator
(12-37004-04) is in place.
When connecting devices to a bus, keep in mind that each device
on the bus must have a unique bus node ID and that you may
need to change a device’s default bus node ID in order to make
it unique. All removable-media device bus node IDs are set via
switches on the device. For information about setting a device’s
bus node ID, refer to the owner’s guide for that device.
3–40 Options and Upgrades