Large Hub Addressing Configurations - Compaq DWZZH User Manual

DWZZH 16–Bit UltraSCSI Hub
removed from the group and at the next arbitration phase, the remaining highest
ID will be serviced. This will continue until all of the IDs in the group have been
serviced once. All requests from IDs not contained in the register will be
"backed off " using ID 7.
Most manufacturers ship host bus adapters with a
default SCSI ID of 7. Ensure that the ID is
changed BEFORE you establish a connection
between the adapter and the Hub.
After all the IDs in the group have been serviced, a new group of IDs will be
captured at the next arbitration phase. The fair arbitration algorithm only applies
to host port SCSI IDs as defined by the assignment in each configuration.
Running the UltraSCSI Hub under heavy I/O with
Fair Arbritration disabled might result in SCSI Bus
starvation for hosts with lower SCSI IDs.
2.2

Large Hub Addressing Configurations

The large UltraSCSI Hub has a specific SCSI ID configuration. The SCSI IDs are
assigned to specific physical locations in the Hub. This allows the fair arbitration
logic in the Hub to correctly identify the SCSI IDs that are participating in a fair
arbitration cycle.
The SCSI ID of each host adapter must
correspond to the assigned SCSI ID of the host
port to which the host adapter is connected.
Mismatched SCSI IDs will cause the SCSI bus to
hang.
Figure 2-1 shows the physical layout of the ports and their associated SCSI ID
assignments.
2–2
CAUTION
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EK–DWZZH–UG. D01