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DWZZH 16–Bit UltraSCSI Hub (Rack-Mountable)
3–2 EK–SMDZS–UG. B01
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.
CAUTION
Running the UltraSCSI Hub under heavy I/O with
Fair Arbitration disabled may result in SCSI bus
starvation for hosts with low IDs.
3.2 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.
CAUTION
The SCSI ID of the HOST adapter must
correspond to the assigned ID of the Hub port, to
which the host port adapter is connected.
Mismatched SCSI IDs will cause the SCSI bus to
hang.
Figures 3-1 and 3-2 show the physical layout of the ports and their associated
SCSI ID assignments on the DWZZH-S5 and DWZZH-09 Hubs.
3.2.1 Narrow Addressing Setting
The large Hub can be used with SCSI bus architectures that are limited to eight
ID assignments such as Digital Unix 4.x and earlier versions (Figure 3-5 shows
narrow ID assignments). A jumper on the rear of the Hub (Figure 3-6) must be
installed to make the Hub respond to SCSI IDs 3 – 0 on the host ports. It should
be noted that the DWZZH-09 Hub cannot be put into a narrow addressing mode.