Technical data

Table 3–3: DS-DWZZH UltraSCSI Hub Maximum Configurations
DS-DWZZH-03 DS-DWZZH-05 Disk Drives
a
Personality
Module
bc
500
Not Installed
400
Installed
303
Installed
204
Installed
105
Installed
020
Not Installed
310
Not Installed
211
Installed
112
Installed
013
Installed
a
DS-DWZZH UltraSCSI hubs and disk drives may coexist in a storage shelf. Installed disk drives are
not associated with the DS-DWZZH UltraSCSI hub SCSI bus segments; they are on the SCSI bus that
is connected to the personality module.
b
If the personality module is installed, you can install a maximum of four DS-DWZZH-03 UltraSCSI hubs.
c
The personality module must be installed to provide a path to any disks that are installed in the storage
shelf.
3.6.1.2.2 DS-DWZZH-05 Fair Arbitration
Although each cluster member system and storage controller that are
connected to an UltraSCSI hub are on separate SCSI bus segments, they
all share a common SCSI bus and its bandwidth. As the number of systems
accessing the storage controllers increases, the adapter with the highest
priority SCSI ID will probably obtain a higher proportion of the UltraSCSI
bandwidth.
The DS-DWZZH-05 UltraSCSI hub provides a fair arbitration feature that
overrides the traditional SCSI bus priority. Fair arbitration applies only to
the member systems, not to the storage controllers (which are assigned
higher priority than the member system host adapters).
You enable fair arbitration by placing the switch on the front of the
DS-DWZZH-05 UltraSCSI hub to the Fair position. (See Figure 3–4.)
Fair arbitration works as follows. The DS-DWZZH-05 UltraSCSI hub is
assigned the highest SCSI ID, which is 7. During the SCSI arbitration phase,
the hub, because it has the highest priority, captures the SCSI ID of all host
adapters arbitrating for the bus. The hub compares the SCSI IDs of the host
adapters requesting use of the SCSI bus, and then allows the device with the
highest priority SCSI ID to take control of the SCSI bus. That SCSI ID is
removed from the group of captured SCSI IDs prior to the next comparison.
3–12 Shared SCSI Bus Requirements and Configurations Using UltraSCSI Hardware